Odd Issue With Ph And Alkalinity

[myarcticsummit]

Hi all,

I recently got a new hot tub and I'm having some issues regulating the pH and TA.

A little background about the water. The tub holds 377 gallons of water and us using an onzen salt system.

We filled the tub using one of the higher quality pre-filters and treated the tub with metalgon before adding any salt or other chemicals. Both salt and chlorine are within acceptable levels. here's how it breaks down.

Salt is within the 1200 - 1500 ppm (onzen v8)

free chlorine: 1.56ppm (recommended 1-3)

pH: 7.8

TA: 90.

Calcium is 160ppm

The issue is, if I use pH Down to lower the PH to get it where I need it, this also lowers the TA which is expected. But then raising the TA back up is then also driving the PH back up!

Example:

Ph lowered to 7.3 this also lowerd the TA down to 46ppm.

I then added a few capfuls of the Alk up and this brought the TA back to 90, but doing this increased the PH back to 7.8!

The PH was lowered slowly, cap full by cap full and running the pumps 15 mins. between testing with a colorQ test kit. Generally after each adjustment I'll run the tub for 15 mins to make sure it can mix well etc.

I just can not get the TA up to it's acceptable range without increasing the PH too much.

Any ideas?

[chem geek]

If your pH is tending to rise, then you should LOWER YOUR TA LEVEL. TA is not just a pH buffer, but is a SOURCE or rising pH because TA is a measure of the over-carbonation of the water and the outgassing of carbon dioxide raises the pH (with no change in TA).

What you are doing is the classic vicious cycle of adding acid that lowers both pH and TA and then adding baking soda that raises TA again causing the pH rising rate to increase. The solution is to not raise the TA. Having the TA at 50 ppm is perfectly OK. You can add additional pH buffering without the side effect of rising pH from carbonates by adding 50 ppm Borates instead. You can do this by using boric acid from DudaDiesel or The Chemistry Store. In 377 gallons you would add 21 fluid ounces volume (or 22 ounces weight) of boric acid. You would only do this after lowering the TA to 50 ppm first.

Also, you didn't report any Cyanuric Acid (CYA) level. Did you add any CYA or any chlorine that adds CYA such as Dichlor when you set up your spa? If not, then the chlorine from the saltwater chlorine generator will be too strong. I recommend having at least 20 ppm and preferably 30 ppm CYA in the spa. Then the 1-3 ppm FC will not be too harsh on spa components nor on your swimsuits, skin, and hair.

By the way, something is wrong with your ColorQ measurements. It would take 5.7 ounces weight (3.8 fluid ounces volume) of dry acid in 377 gallons to lower the TA from 90 ppm to 46 ppm, but that would lower the pH from 8.0 down to 6.3 (though carbon dioxide outgassing would prevent it getting that low for very long).

[myarcticsummit]

The PH seems to have stabilized...(what I did was get the alk setup a little on the high side first.. then adjusted the Ph to get that in range.... thus keeping the TA in it's proper range) Seems to be holding in it's current state the last 48hrs. or so with about 2 hrs of use.

Current numbers as of this morning are:

ph: 7.4

TA: 90

FCL: 2.0

However, the water is slightly cloudy... very slight. I do have some iron in the water as well. Had a local pluming supply check for iron as I noticed a very slight discoloration too. I treated the tub with metal gon during the initial fill.... but have since added a slight amount of water due to normal loss. Is there something I can treat it with to "filter" out the iron? More metalgon?

My current CYA level is 5.0 ppm. I did not add any CYA when filling the tub or use and dicholor. The tub was filled with a higher quality pre-filter as well. What product do I need to increase the CYA?

Thanks for the help.

The quest for perfectly crystal clear water continues!

[chem geek]

There are pre-filters you can use like MetalTrap.

As for your pH, it will go up if you have aeration and decide to use bleach at some point. If you use only Dichlor, then you might be OK. If you use non-chlorine shock (MPS) then that's the most acidic.

You don't actually have any CYA in the water. The 5.0 ppm is a false reading. For every 10 ppm Free Chlorine (FC) added by Dichlor, it will increase your Cyanuric Acid (CYA) by 9 ppm. That's the easiest way to increase CYA over time, but if you use only Dichlor then the CYA will keep building up making the chlorine less effective.

[myarcticsummit]

I should make a correction. This is the Chlorine I'm using: http://www.spapureusa.com/index.php/products/sanitizers/granular-chloride/ which does have the Dichlor in it. I do add small amounts of this from time to time.

Numbers as of this morning:

FCL: 1.18

ph: 7.6

alk: 87

CYA: 16

CH: 157

Adding a little CYA help make the water feel a little less harsh.

I guess at this point what would you suggest I do? The main issue at this time is water that is slightly cloudy. Are my numbers that far out of range?

The water is nearly a week old and was filled using a pre-filter and treated with metalgon. Just needs more time to filter and "self clear"? FCL too low?

Thanks for all your help.

[chem geek]

According to their MSDS, it's 97% pure Dichlor. So yes, as the CYA builds up the water will feel less harsh, but as the CYA continues to build up the chlorine will become less and less effective. This is why we came up with the Dichlor-then-bleach method. You use Dichlor initially to build up the CYA to around 30 ppm and then you switch to using unscented plain (not splash-less or outdoor) bleach as your source of chlorine. About once a month you use Dichlor for a day or two to add around 5 ppm CYA to the water since chlorine slowly oxidizes CYA.

However, if you do switch to using bleach, you have to get your TA down to around 50 ppm or even lower and need to use 50 ppm Borates (from boric acid, such as from DudaDiesel or The Chemistry Store. By using bleach instead of only Dichlor, you can usually go at least twice as long between water changes. You also reduce the risk of getting hot tub itch/rash/lung.

Your current numbers are OK while you are using Dichlor. As the CYA rises you could target 2 ppm FC or so but most people like starting out their soak with 1-2 ppm FC to minimize chlorine/chloramine smell. As I noted above, if you decide to switch to bleach after the CYA gets to 30 ppm or so then you'll want to lower the TA (via acid addition and aeration) and use the 50 ppm Borates for additional non-carbonate pH buffering.

As for adding chlorine after a soak, the very rough rule-of-thumb is that every person-hour of soaking in a hot (104ºF) tub without an ozonator requires 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize the bather waste. With an ozonator you may need half this or less. You need to add additional chlorine in between soaks to maintain a residual if you don't soak every day or two. Note that while ozone oxidizes bather waste, it also reacts with chlorine so an ozonator is great if you soak every day or two and not so great if you don't (at least when using chlorine)

[myarcticsummit]

Here's another question. I'm curious if my filters are working properly. Take a look at the following photo of a sample of water:

http://www.wphdev.com/water.jpg

I'm able to monitor the spa so I can see it's supposedly filtering each day during it's allotted time. I've even tried bumping up the filter time and nothing seems to remove it!

[chem geek]

See if you can capture the flakes and if you can, then add a little vinegar to them. If they fizz, then they are calcium carbonate. According to the water chemistry numbers that you posted, you shouldn't be getting such flakes, but those numbers don't seem to be from your own good Taylor K-2006 test kit so they are suspect. If the pH, TA, or CH are higher than indicated, then the saltwater chlorine generator (onzen salt system) could be creating some of those flakes. Calcium carbonate forms at the high pH hydrogen gas generation plate and then when the polarity is reversed (which it is every so often automatically by the onzen salt system) the calcium carbonate scale flakes off.

You can lower your TA closer to 50 ppm and you can also add 50 ppm Borates (using boric acid) as I had indicated in my earlier post. Basically, you can operate your onzen salt system with the same water chemistry as recommended for the Dichlor-then-bleach method. The salt system would provide a background level of chlorine in between soaks while you would add bleach (assuming CYA is already at 30 ppm) after longer soaks or soaks with multiple people.

[myarcticsummit]

Thanks for the reply. Those flakes are so small I just can't seem to capture them. I tried adding some vinegar directly to a small sample of water to see if it would bubble but I didn't see anything. The test kit I'm using is the colorQ 7.

I should get my number verified at my local dealer and see what they say. They have a kit by the same company... just tests more things.

I was able to get a flake off the side of the tub at the waterline... and put this in vinager... but not flakes. There is like a white ring around the tub as well and it kinda has a "smeary" feel to it. You can see the ring more obviously in areas where the water is not as disturbed as much when the pumps are running. In the seating areas it's almost non existent.. or at least I can't see it. So it appears to be a build-up of some kind.

[chem geek]

The ColorQ is not terrible, but it is not accurate for all readings. If you want accurate testing, then the Taylor K-2006 test kit would be the one to use.

Since this hot tub is fairly new, you might just have greases/oils and/or biofilms in the plumbing. You can use Ahh-Some just before your water change to remove such biofilms. One doesn't have the water last very long before the first water change in a new spa.

[myarcticsummit]

I did an experiment last night. I took a quart sample of water in a mason jar... I then added some non-chlorine shock to it and shook it around for a bit. Within a couple of minutes of doing that.. the water cleared up substantially!

I'm suspect now if my onzen is able to keep up? I've had it set on 14hrs per day and so far I'm the only user of the tub about 1/2 per evening.

The only way I've been able to get decent FCL numbers is to add my dichlor now and then... but I have not checked it immediately before or after use.

All I know right now is that shocking the tub seems to be clearing it up!

[chem geek]

It does sound like your Onzen system isn't outputting enough, but keep in mind that such salt systems aren't designed to output enough to handle larger spa bather loads. They are designed to provide a background level of chlorine and can handle low or possibly moderate bather loads (depending on the sizing of the system). One person for 30 minutes would need around 3.25 ppm FC in your 377 gallon spa.

The Onzen manuals I've seen talk about an ozonator in the system as well. Ozone will break down chlorine so maybe the ozonator is on too long and using up the chlorine that is generated. See this manual for some procedures checking to see if the saltwater chlorine system is working and if the ozonator is working.

[myarcticsummit]

Thanks for the reply. That's what I'm seeing too and in the manual they do talk about adding some boost now and then. I guess if it can't keep up then what's the point of having it? Might just drain the tub and refill and not have a salt system at all?

I'll try bumping it up too. Seems the point of a salt system is just for more "background cleaning" while it's not in use.

I will double check to see if it's working properly. I've been able to see the "smoke" it talks about but I'll do a more detailed check of the system I think. I really can't believe it's this "useless" or at least seems that way as of now.

Here's a question. Why does the Non-chlorine shock seem to raise the FCL level even though it contains now chlorine? False reading?

[chem geek]

Yes, the MPS will register on chlorine tests, either as FC or CC depending on the type of test.

[myarcticsummit]

It does make the reading high when doing the FC test. Is there a way to determine how much actual FC there is or will I need to wait to let that normalize?

Does the MPS work as well for shocking as does granular chlorine?

[chem geek]

Yes, you can use the Taylor K-2042 to distinguish between chlorine and MPS.

MPS doesn't oxidize the same chemicals as chlorine though there is some overlap. Usually people using MPS with silver ions such as with Nature² find that they need to use chlorine once a week or so to keep the water clear. Note that use of MPS alone without silver ions is NOT a disinfectant.

[myarcticsummit]

Do you recommend I stop using the MPS to "shock" with?

My current CYA level is around 30ppm should I start using the bleach? How much would I use if I have the onzen system?

The water is still not crystal clear as I would like... which I think it may be just because it's the tubs first fill and there just seems to be these floating fibers and 'dust" like particles. The white flakes are gone and have not come back since I've cleaned the ring from around the tub - my guess bio-films of some sort.

Does't matter how much I seems to filter it just never get's perfectly clear - even with applications of MPS after each soak. Perhaps I should be using chlorine? You've mentioned the borates would that help in that area as well as far as clarity?

[chem geek]

If you are using chlorine, then there should be no need for you to use non-chlorine shock (MPS).

With your CYA at 30 ppm, you can start using bleach IF you get your TA lower to around 50 ppm and have/add 50 ppm Borates.

As for how much bleach to add, you can start with the rule-of-thumb I gave in the earlier post and then cut back or adjust as needed so that you start your next soak with a low but measurable chlorine level. If you were to soak regularly with consistent bather load, you could turn up your Onzen system and add less bleach, but if you vary your frequency and length of soaking then you are better off setting the Onzen to provide a background chlorine dose and use bleach to handle your bather load.

For clarity, filtration is most important. The chlorine will tend to keep the water clear better than MPS, but you should be filtering enough to remove particles from the water. If you're not getting good filtration and the circulation pump is on long enough, then you should check your filters to make sure they aren't torn or have other problems.

[myarcticsummit]

I'm filtering at 6 hrs. per day. 2 - 3 hr. sessions.

I'll try some new filters because I sometimes notice a fiber that looks like it's a fiber from the filter. To short to be a hair or something.