Can't Maintain Residual Fc - Ozone To Blame?

[TheMo]

Hi. I have an '07 Sundance Cameo, purchased as the last '07 display model in August '08. The tub has ozone, nature2 and I use dichlor to sanitize. The problem I have always had is maintaining any residual FC.

The water right now is 2 months old, crystal clear, has no odors. The dealer feels that water being balanced and so nice and clear is all I need to be concerned with. He shrugs my concern off and says that the ozone and nature2 along with a weekly shock will handle all my needs. This message board, however, has convinced me otherwise.

I shock weekly to 10ppm FC (taylor test kit) use mps as a boost when needed, and use 1tsp dichlor per person per hour following tub use. My concerns about residual FC being at or near 0 have always troubled me, but yesterday, following the weekly shock, within 8 hours I had 0 FC. Usually there is a residual 1 - 3pmm the day after shocking.

The tub is used a couple times a week, often times by myself alone, so the bather load is light.

I keep the water balanced roughly to the following:

pH ~ 7.5

TA ~ 60

CYA creeping up to 100

CH 100

I've read that ozone will dissipate the FC. To what extent does this occur and, other then my tub being diseased, could the ozone be the culprit?

[Hillbilly Hot Tub]

With nature 2 and ozone, you need only a .5 risdual of chlorine. As your CYA goes up, you will need a higher and higher chlorine risdual since the CYA makes chlorine less effective which is part of why many people use MPS at each use and shock weekly or biweekly with dichlor, to keep the CYA level down.

If you chlorine level is dropping, not holding a risdual, then you need to use more chlorine, you are not using enough to oxidize all the wastes and leave a little bit to keep a risdual

What is your combined chlorine level? I am guessing it is high, if the combined (total) chlorine is higer than your free chlorine, you need to super shock.

Some people have noticed ozone effects their chlorine, others have not. I use more chlorine when my ozone died than when it was working because the ozone was oxidizing wastes, leaving my chlrine to do its sanitizing rather than oxidizing.

[TheMo]

I'll try super shocking. How high should I go fc ppm to super shock?

My combined chlorine measured 0.6ppm a week ago.

[Hillbilly Hot Tub]

I'll try super shocking. How high should I go fc ppm to super shock?

My combined chlorine measured 0.6ppm a week ago.

You can shock with chlorine or MPS. I would suggest to use MPS, this will not raise the CYA any higher, you are allready on the high side and MPS oxidizes wastes really well. I would double the dose of MPS that you use, 2 ounces is usually what people shock with for a standard size tub, I would do 4 ounces. MPS burns off fairly quickly. Clean the filters out really well, then add your chlorine to see if you can maintain a reading for 24 hours.

If you use chlorine, I would bring to 10-15 ppm, if it is gone in 8 hours, bring it to 10-15 ppm again. This is going to raise the CYA though.

[Nitro]

I'll make a suggestion. Instead of shocking with Dichlor, shock with bleach. It won't raise your CYA. However, if I were you, I'd just drain the tub and start over. Your CYA is getting too high. If you want to try a method that doesn't raise CYA too high, read THIS. You can still use the Nature2 system, but the only difference is, you switch to bleach after your CYA gets to 20-30ppm.

Also, I'd read THIS about Chlorine Demand (CD). Your CD is 100% right now. The only way to get it down is to start shocking. However, you may find it difficult to get it down to an ideal level without doing a lot of shocking. CD is something you should keep track of, so it doesn't get too high.

[TheMo]

The super shock has definitely done something. I added the 4 ounces of mps yesterday and then 1 tbs of dichlor later in the evening. My reagents bleached to yellow instead of clear while doing the fc check today so I suspect the chlorine is high? The color change occurred at 8ppm fc. Also, my pH is down to 7.0. I've got the tub running wide open with all jets, aerators and blower running and will check again later on.

In any case, reading fc the next day is vast improvement! Thanks Hillbilly Hot Tub.

Nitro - I'm planning on using your bleach method after my next water change. I need a nice day and some free time to drain the tub and those are hard to come by this time of year, but hopefully within a month. Thanks for the input, it's much appreciated.

[Nitro]

The super shock has definitely done something. I added the 4 ounces of mps yesterday and then 1 tbs of dichlor later in the evening. My reagents bleached to yellow instead of clear while doing the fc check today so I suspect the chlorine is high? The color change occurred at 8ppm fc. Also, my pH is down to 7.0. I've got the tub running wide open with all jets, aerators and blower running and will check again later on.

Also keep in mind MPS is acidic and will lower your TA/pH, especially if a lot is used. That's the main reason I don't recommend shocking a lot with MPS. I would just use bleach.

If your pH doesn't come up from aeration, you may need to add Baking Soda. Check your TA to see where it's at. Hopefully you didn't lower it too much. Keep aerating though.

Nitro - I'm planning on using your bleach method after my next water change. I need a nice day and some free time to drain the tub and those are hard to come by this time of year, but hopefully within a month. Thanks for the input, it's much appreciated.

I think you'll find the Dichlor/Bleach method to be much better. Also, don't forget to track your Chlorine Demand (CD). It will help you gauge your progress.

[Raegor]

With nature 2 and ozone, you need only a .5 risdual of chlorine. As your CYA goes up, you will need a higher and higher chlorine risdual since the CYA makes chlorine less effective which is part of why many people use MPS at each use and shock weekly or biweekly with dichlor, to keep the CYA level down.

So Hillbilly, I have the Hotsprings Silver ion + Ozone which I assume from what I've read is the same as nature2. Can I keep a minimal .5 fc level as well? I've been trying to maintain 3 which is what most everything I've read says...

Thanks

[cofive]

Hi. I have an '07 Sundance Cameo, purchased as the last '07 display model in August '08. The tub has ozone, nature2 and I use dichlor to sanitize. The problem I have always had is maintaining any residual FC.

The water right now is 2 months old, crystal clear, has no odors. The dealer feels that water being balanced and so nice and clear is all I need to be concerned with. He shrugs my concern off and says that the ozone and nature2 along with a weekly shock will handle all my needs. This message board, however, has convinced me otherwise.

I shock weekly to 10ppm FC (taylor test kit) use mps as a boost when needed, and use 1tsp dichlor per person per hour following tub use. My concerns about residual FC being at or near 0 have always troubled me, but yesterday, following the weekly shock, within 8 hours I had 0 FC. Usually there is a residual 1 - 3pmm the day after shocking.

The tub is used a couple times a week, often times by myself alone, so the bather load is light.

I keep the water balanced roughly to the following:

pH ~ 7.5

TA ~ 60

CYA creeping up to 100

CH 100

I've read that ozone will dissipate the FC. To what extent does this occur and, other then my tub being diseased, could the ozone be the culprit?

If at all possible I too would like some info on the affect of ozone on FC. We seem to have gotten a bit away from the original question for this thread. I appreciate all the expertise and opinions here guys, but can we get an answer to the question?

[Nitro]

If at all possible I too would like some info on the affect of ozone on FC. We seem to have gotten a bit away from the original question for this thread. I appreciate all the expertise and opinions here guys, but can we get an answer to the question?

An Ozonator will cause FC to drop faster, because of outgassing. However, the ozonator will help Chlorine oxidize waste, so it's hard to tell the impact. The OP was losing 10ppm FC in 8 hours. That's way more than an Ozonator should drop it.

If I were betting man, I'd bet an Ozonator will increase Chlorine Demand (CD) by around 20%. I don't have an Ozonator, so I can't test it. Maybe someone with an Ozonator can test their CD on a fresh fill, and report back to us. Cofive?

[TheMo]

24 hours after adding 1 tbs of dichlor my FC is 5.5ppm.

Still not sure what affect the ozone may be having on my FC dissipation, but its a boat load less then a tub in need of a super shock.

Thanks again for the advice. You guys rock.

[chem geek]

Also keep in mind MPS is acidic and will lower your TA/pH, especially if a lot is used. That's the main reason I don't recommend shocking a lot with MPS. I would just use bleach.

Bleach will raise the pH until the chlorine gets used up so the pH will slowly drop after adding it. With a TA of 80 ppm (and CYA of 30 ppm) and starting pH of 7.5, adding 10 ppm FC using bleach will initially raise the pH to 8.1 so if you are going to be shocking with bleach it's best to lower the pH first.

The amount of non-chlorine shock (MPS) that is equivalent to adding 10 ppm FC would lower the pH from 7.5 to 7.38 with the same starting parameters above.

The adding of 1 tablespoon of Dichlor with 4 ounces (I assume volume) of MPS would lower the pH from 7.5 to 7.18 initially and the FC would have risen by 5.9 ppm. After the chlorine dropped back down, the pH would drop to 7.04. The amount of MPS used is equivalent to 23 ppm FC. If you used only bleach for this combination of 6+23=29 ppm FC, then the pH would have risen to 8.58 which is pretty darn high and could cause scaling.

Basically, if you are going to shock with a very high FC or FC-equivalent, I wouldn't use just bleach unless you had 50 ppm Borates in the water. In that case, the pH would rise from 7.5 to 7.91 which is more reasonable.

Richad

[Nitro]

Bleach will raise the pH until the chlorine gets used up so the pH will slowly drop after adding it. With a TA of 80 ppm (and CYA of 30 ppm) and starting pH of 7.5, adding 10 ppm FC using bleach will initially raise the pH to 8.1 so if you are going to be shocking with bleach it's best to lower the pH first.

The amount of non-chlorine shock (MPS) that is equivalent to adding 10 ppm FC would lower the pH from 7.5 to 7.38 with the same starting parameters above.

The adding of 1 tablespoon of Dichlor with 4 ounces (I assume volume) of MPS would lower the pH from 7.5 to 7.18 initially and the FC would have risen by 5.9 ppm. After the chlorine dropped back down, the pH would drop to 7.04. The amount of MPS used is equivalent to 23 ppm FC. If you used only bleach for this combination of 6+23=29 ppm FC, then the pH would have risen to 8.58 which is pretty darn high and could cause scaling.

Basically, if you are going to shock with a very high FC or FC-equivalent, I wouldn't use just bleach unless you had 50 ppm Borates in the water. In that case, the pH would rise from 7.5 to 7.91 which is more reasonable.

Richad

TheMo has a TA of 60ppm, and a CYA near 100ppm. Bleach is the way to go in this case. Large amounts of MPS will lower pH/TA too much. No?

However, if TA is 80, then yes bleach by itself would raise pH. I guess I should have been a little more clear in that statement.

[chem geek]

TheMo has a TA of 60ppm, and a CYA near 100ppm. Bleach is the way to go in this case. Large amounts of MPS will lower pH/TA too much. No?

However, if TA is 80, then yes bleach by itself would raise pH. I guess I should have been a little more clear in that statement.

Using bleach for sanitation and oxidation, that is for normal daily use, is fine (with some CYA in the water, of course) once you've got your TA at a place where you aren't seeing a lot of pH rise. My comment was with regard to shocking with high levels. The addition of bleach will make the pH rise initially so adding a lot of bleach will make the pH rise a lot -- too much unless you have 50 ppm Borates in the water. So for shocking to get rid of a lot of accumulated bather waste, if you are going to use bleach then you'd need to lower the pH substantially first (unless you have the Borates) or you need to use MPS or a combination of MPS and bleach. I was not suggesting to use Dichlor which would raise the CYA level.

In any event, as the higher FC level drops, the pH will drop so then you have to be careful in the other direction, but since the pH will often rise from aeration, this is less of a problem. Note that my calculations with MPS include the small amount of magnesium carbonate usually found in non-chlorine shock product which is why it's not as acidic as you might first expect. Yes, MPS will lower the pH if you use a lot, but as I showed, it doesn't quite get into the danger zone as readily as bleach does on the high end of pH.

Specifically for TheMo with a TA of 60 ppm and a CYA near 100 ppm, 1 tablespoon of Dichlor with 4 ounces volume of MPS in 350 gallons would lower the pH from 7.5 to 7.24 and then when the 5.9 ppm FC from the Dichlor got used up, the pH would drop to 7.12 (my calculations have the MPS get used up immediately in its pH effect -- in reality, the pH won't drop the full amount upon addition and some of it will drop over time, somewhat similar to chlorine, though MPS does have some initial acidity). So somewhat lower than I calculated earlier, though not by that much. If you used the equivalent amount of bleach for this Dichlor/MPS combination, that would be 29 ppm FC where the pH would rise from 7.5 to 8.95 initially so even worse than I had previously calculated (because the TA is lower) and at a great risk for scaling. If you had 50 ppm Borates, then the pH would rise to 7.95 which is manageable. Yes, as the FC drops, the pH will come back down, but that doesn't happen right away and in the meantime the water (without Borates) is at a great risk of scaling.

It seems to me that if one is gong to use Dichlor-then-bleach and especially when they anticipate needing or wanting to shock using bleach, then one really should have 50 ppm Borates in the water (from ProTeam Gentle Spa, for example). So to more easily manage the Dichlor-then-bleach method, you should not only have a lower TA, but use 50 ppm Borates as well. That would make the system easier and less likely to have problems from people accidentally just adding bleach without thinking about the consequences.

Richard

[Nitro]

Richard,

When I said shock with bleach, I meant bringing FC to 10-12 ppm, not 29 ppm. 30 ppm FC would obviously cause problems, unless you drained it right way (i.e. Decontamination).

TheMo's pH was 7.0 last measurement. I'm curious to know where TA is at. How much will 4oz MPS drop TA?

[chem geek]

Richard,

When I said shock with bleach, I meant bringing FC to 10-12 ppm, not 29 ppm. 30 ppm FC would obviously cause problems, unless you drained it right way (i.e. Decontamination).

TheMo's pH was 7.0 last measurement. I'm curious to know where TA is at. How much will 4oz MPS drop TA?

The TA would only drop around 2 ppm.

Even 10 ppm FC of bleach added to 80 ppm TA, 30 ppm CYA water will raise the pH from 7.5 to 8.12. If the TA is 60 ppm, it rises to 8.30. If you use 50 ppm Borates and have a TA of 60 ppm, then it rises to 7.75.

[Nitro]

Even 10 ppm FC of bleach added to 80 ppm TA, 30 ppm CYA water will raise the pH from 7.5 to 8.12. If the TA is 60 ppm, it rises to 8.30. If you use 50 ppm Borates and have a TA of 60 ppm, then it rises to 7.75.

Yes, but doesn't pH drop back down after FC gets used up?

[chem geek]

Even 10 ppm FC of bleach added to 80 ppm TA, 30 ppm CYA water will raise the pH from 7.5 to 8.12. If the TA is 60 ppm, it rises to 8.30. If you use 50 ppm Borates and have a TA of 60 ppm, then it rises to 7.75.

Yes, but doesn't pH drop back down after FC gets used up?

Yes, unless aeration has kept the pH up, but in the interim, the pH is high so there could be some scaling possibility though it's not for very long. Initially, the chlorine may combine with ammonia to form monochloramine and that raises the pH even more, though not by that much (from 8.30 to 8.44) and then as that monochloramine gets oxidized to nitrogen gas the pH comes down, but that can take about an hour or so. Chlorine does not oxidize bather waste immediately -- it takes time -- and this is especially true if you aren't soaking with chlorine. If you are soaking with sufficient chlorine, then the bather waste partly gets taken care of during the soak so the pH won't rise as much.

If you are only shocking or using 10 ppm FC, then starting out with a pH of 7.2 would at most raise the pH to 7.76 even including the rise if there was ammonia. The more serious problem would be the very heavy shocking that was described with 4 ounces of MPS due to falling behind with keeping up with bather load. People just shouldn't think they can add large amounts of bleach and if there is that possibility of people doing that, then 50 ppm Borates at least minimizes the risk of scaling. Heavy bather load would be such a situation since larger amounts of bleach would be used if that was the only oxidizer.

Richard

[TheMo]

Richard,

When I said shock with bleach, I meant bringing FC to 10-12 ppm, not 29 ppm. 30 ppm FC would obviously cause problems, unless you drained it right way (i.e. Decontamination).

TheMo's pH was 7.0 last measurement. I'm curious to know where TA is at. How much will 4oz MPS drop TA?

My TA was measured at 50 following the shock with 4 oz MPS - down from the original of 60. 3 tbs of baking soda and an hour of aeration had the TA reading 60. The tub was then covered for the rest of the day.

The next day's testing provided the following results:

FC 1.4ppm

CC 0.2ppm

pH 7.4

TA 80

[chem geek]

In theory, the 4 ounces volume of MPS (in 350 gallons) would lower the TA by only around 3 ppm by itself, but the addition of 1 tablespoon of Dichlor increases the TA by about 2 ppm and the consumption of that chlorine reduces the TA by about 4 ppm. So the net of all of this is a reduction of TA of around 5 ppm which can show up as 10 ppm in a test since that is the test's resolution. Some of these changes in TA are due to changed in pH while some are due to the chlorine (hypochlorite ion counts towards TA).

[Hillbilly Hot Tub]

With nature 2 and ozone, you need only a .5 risdual of chlorine. As your CYA goes up, you will need a higher and higher chlorine risdual since the CYA makes chlorine less effective which is part of why many people use MPS at each use and shock weekly or biweekly with dichlor, to keep the CYA level down.

So Hillbilly, I have the Hotsprings Silver ion + Ozone which I assume from what I've read is the same as nature2. Can I keep a minimal .5 fc level as well? I've been trying to maintain 3 which is what most everything I've read says...

Thanks

As far as I know you can keep the .5 risdual with the hotsprings stick also. I would suggest if you have guests using the tub that you bring it back up when they are using it. The point 5 is the minimum, and I would only have it at that for my husband and I. If my kids use it, I have it at 2, if guests use it I have it at 5. This is also using MPS at each use and shocking(to 10 ppm) once per week with chlorine. If I did not use MPS at each use, I would not keep it that low.

[chem geek]

I think what is particularly important is that you use enough oxidizer and sanitizer so you add enough after your soak to be able to maintain a residual FC that is still measurable by the next time you get into the tub. If the sanitizer level drops to close to zero, then there is the risk of bacterial growth. Such risk is greatly reduced when using a metal ion system, but it is not eliminated and the time to kill bacteria quickly before they can form biofilms is either during your soak or immediately afterwards (your skin, mucous and fecal matter shed a lot of bacteria).

The number one reason for reports of hot tub itch/rash/lung seems to be people not using enough oxidizer/sanitizer for their bather load. The use of metal ion systems helps, but doesn't eliminate this issue. The second reason seems to be a reduced sanitizer level from continued use of Dichlor which builds up Cyanuric Acid (CYA) reducing the active chlorine level. This seems to be more of a problem when metal ion systems aren't used.

Richard

[Nitro]

In theory, the 4 ounces volume of MPS (in 350 gallons) would lower the TA by only around 3 ppm by itself, but the addition of 1 tablespoon of Dichlor increases the TA by about 2 ppm and the consumption of that chlorine reduces the TA by about 4 ppm. So the net of all of this is a reduction of TA of around 5 ppm which can show up as 10 ppm in a test since that is the test's resolution. Some of these changes in TA are due to changed in pH while some are due to the chlorine (hypochlorite ion counts towards TA).

I don't mean to question your math, but a TA of 50ppm is about what I expected. From my experience, using MPS (even in small dosages 1oz/week) would lower my TA/pH (50/7.2) to the point where I'd need to add a little Baking Soda. That's the reason I haven't used MPS on this fill. I want to control my TA.

Also, it must take a long time for scale to develop. I've done two decontaminations (FC=100ppm), and never had a hint of scale forming. You can do the math of adding (100ppm FC of bleach). I've also shocked my own tub to 12-15ppm with bleach regularly, before I used borates, and never had a problem with scaling. That's when I first started using the Bleach method, and was using way more than I needed to.

Just my observations.

[chem geek]

I think you may be right that I am figuring on more effect from magnesium carbonate than is correct. I think I may have used the MSDS pH to figure what was going on, but neglected to account for having HSO₅^- remain together and not dissociate. I'll double check the calculations. If there were no extra base effect, then after MPS gets used up the 4 oz. in 350 gallons would drop the TA by almost 25 ppm. I'll work on this and update my numbers. I need to separate out the MPS addition from MPS usage as well. Thanks for questioning it.

I also suspect that different MPS brands may pH balance their products by different amounts. This may explain why some are not 43% potassium monopersulfate.

Richard

[Nitro]

From what I remember it didn't take much longer than a couple weeks before I needed to add Baking Soda. I was adding ~1oz of MPS per week. My TA was around 60ppm to start, then dropped to around 50. My pH dropped to around 7.2, and wasn't rising very much with aeration. I just decided to add a little BK to raise my TA back to 60 and be done with it.

Again these were just my casual observations at the time. I didn't do any detailed calculations or documentation. I'm just going by memory, which isn't the greatest these days. I'll be interested to see what you come up with though.