Tf-100 1st Test

[John Quincy]

350 gallon spa

Received Taylor TF-100 yesterday and tested this morning (approx 9 hours after last adding dichlor):

PH 7.5

FC 7.5

CC 2.0

CYA 30-35

T/A 120

CH 120

Everything looks good except for CCs at 2ppm.

I am also wondering how CYA could already be at 30-35 ppm after only 10.5 tsp of dichlor.

Below is a log of dichlor added to date (in tsp):

12/18-->2.0

12/19-->3.0

12/20-->2.5

12/21-->3.0

ttl----->10.5

12/22-->3.0 oz bleach to shock

Spa Usage: Have used every night. 1st night with wife and two kids, after that just myself and daughter (rest of family caught cold). We all have showered before getting into the spa.

Every night before getting into spa, I have been testing. The testing has shown no or little chlorine. So I have added 1 to 1/2 tsp of dichlor 30 minutes before entering. After getting out, I have added additional dichlor to reach 2 1/2 to 3 total tsp per day. To date a total of 10.5 tsp has been added. I know that the normal dose should be 2 tsp but have been adding 3 tsp because the test strips do not detect chloring 24 hours after adding.

Due to this morning's test of 2 PPM CC and 35 PPM CYA, I have switched to bleach and have added 3 ounces of 6% bleach to shock. Since the test indicated 7.5 PPM FC, I am estimating that the bleach will raise FC to 11.5.

As I was basing all my chlorine sanitizer targets on 20 PPM CYA, what should my need targets be for daily chlorine and shock @ 30 to 35 PPM CYA?

Today, I am buying an electronic siphon to drain filter well and will wash filter by hose and in dishwasher (no dry cycle) and clean the cover.

Should I be concerned about the 2 PPM CC? Am I missing something or overdoing anything?

[chem geek]

10.5 teaspoons of Dichlor is around 1.75 ounces weight which would add 21 ppm FC cumulatively and 19 ppm CYA. The CYA test is only accurate to within 10 ppm CYA plus CYA tends to stick to surfaces so I'll bet that between testing error and residual left over CYA (assuming you used Dichlor before this fill and this isn't a brand new spa), then 30 ppm is certainly possible. This is not a problem.

You don't need to be keeping the FC quite so high. 6 ppm FC should be fine at 30 ppm CYA. Nevertheless, your chlorine usage does seem to be on the high side so I would shock with bleach to get to close to 12 ppm FC as it sounds like you will be doing and see if that takes care of the CC. Be sure to keep the spa uncovered for at least an hour after adding the bleach to shock. If you smell a chlorine smell that isn't the fresh bleach smell, then that's some combined chlorine gassing off -- the rest will get broken down by the extra chlorine.

It sounds like you're doing everything right but for some reason have something in your spa that is consuming chlorine faster than normal. Typical usage in a 350 gallon spa is around 3-4 ppm FC but that's usually with 1-2 people and your bather load has been a little higher than that. The higher chlorine level should take care of this extra demand. Also, the CC may just be leftover from the chlorine running out before it broke it all down.

Be sure to keep the spa uncovered after you get out of the spa and add the chlorine each time you use it. Keep the spa uncovered for at least 30 minutes. You are correctly measuring the chlorine, including CC, before you get in.

In the worst case if your bather load demands it, you might be having a higher FC target after getting out in order to have some residual when you next get in (and to avoid CCs). Another option would be using some non-chlorine shock (MPS) regularly to oxidize the organics so that chlorine doesn't have to and that will also lower the chlorine demand, but before going that route try adjusting the chlorine level as you are doing by a shock and then see what happens. Every spa and usage is different, but once you get into a routine it will be fairly consistent and easy.

Richard

[John Quincy]

In my prior post, I neglected to mention that my tub is brand new and I just installed an ozonator on Tuesday before starting it up. From reading some of your prior posts, I can probably conclude that it was installed correctly because it appears that the ozone is depleting the chlorine and giving me false positives for CCs. Is this possible? A good test would probably be to unplug the ozonator and retest for a few days. Since there is not a detectible chlorine smell at 2 ppm cc, something is up.

My apologies for neglecting to mention the ozonator but I was not even sure if it was working or the effects that it would have on my chemistry until reading some of your earlier posts today.

[chem geek]

Ah yes, the ozonator may be depleting the chlorine. I'd see what happens if it is turned off. You can then roughly figure the amount of chlorine that the ozonator is destroying and can just add more to compensate for that when you turn it back on. What is strange, however, is getting Combined Chlorine, especially with an ozonator since it should be oxidizing organics quite readily. I don't think the CCs are a side effect of the ozonator, but there was someone else on this forum who also reported seeing CCs with their ozonator so that is a strange coincidence so might mean that somehow the ozonator is creating measurable CC or otherwise interfering with that part of the test.

By any chance, you aren't using a non-chlorine shock, potassium monopersulfate (MPS), are you? If so, then that measures as CC in the chlorine test, though there is a Taylor K-2041 kit that removes such interference.

Richard

[John Quincy]

No, I am not using MPS. Although I did buy some today, none has been added to the tub. Once I got rid of the elevated CCs with Chlorine shock and had determined the appropriate daily chlorine dose, it was my plan to experiment with preventing CCs via MPS. This was before I read your reply to lilRed where you stated that MPS was not needed in conjunction with an ozonator.

If MPS and ozone generators are both oxygenates that deplete FC, why would only one, MPS, cause CC test conflicts? It will be interesting to unplug it and see how it effects my tests. We are in the middle of a snow storm so the experiment will probably have to wait for a day or two.

One of the selling points to ozonators is the ability to keep the water clean with less chemicals. This seems to be the opposite case. I will most likely have to significantly up chlorine doses because the ozone is apparently depleting them so rapidly.

Is there an advantage to using bromides with ozonators? Does ozone deplete bromides? If not, one probably could use less and still have clean water.

It sure is strange that the water appears crystal clear with no chlorine smell with elevated CCs and no detectible FC after 24 hours. I guess one could have worse problems with a spa than clear water.

[chem geek]

Actually, MPS does not deplete FC because the strength of this oxidizer is very close to that of chlorine so they pretty much do not react with each other. Ozone is a far stronger oxidizer so is able to oxidize chlorine (turning it into chlorite and then chlorate).

The fact that MPS shows up as CC is only due to the unique nature of the CC test which works as follows:

1) DPD powder is added to water sample and the Free Chlorine (FC) in that water combines with the DPD indicator to turn it pink/red.

2) Ferrous Ammonium Sulfate (FAS) drops reduce the chlorine (the chlorine oxidizes the FAS) removing the chlorine from the indicator until it turns clear.

3) The third reagent is iodide which reacts with the chlorine in Combined Chlorine (CC) to get oxidized to iodine (the chlorine oxidizes the iodide to iodine) and the iodine combines with the indicator to turn it pink/red. If there is MPS present, then it can oxidize the iodide to iodine making it look like there is CC when it is really MPS.

The Taylor kit that removes this interference probably by selectively reducing or otherwise inactivating the persulfate without affecting the rest of the test. This is done very early on right after DPD powder is added in the test so that the MPS doesn't affect either the FC or CC parts of the test.

You are right that the selling point about ozonators using less chemicals isn't necessarily true in a chlorine pool/spa -- it depends on whether the ozone is oxidizing organics vs. oxidizing chlorine. It is more true in a bromine situation since the ozone just reactivates bromide to bromine, but can also oxidize bromine to bromate which isn't good (it's a possible carcinogen, mostly in terms of drinking water).

The CCs are probably not chloramines if you don't smell anything. They could be chlorine combined with some other organics that are not volatile or it could be a false test for some reason. If there were enough ozone lingering in the water during the test, then it could act as the oxidizer to oxidize iodide to iodine and register as CC. Ozone doesn't last very long, however, so if you take your sample away from (not near) a return and let it sit (covered) for a few minutes then perhaps the ozone will dissipate and will not measure as CC -- if that is what is going on. Maybe your ozonator is exceptionally powerful which would explain the destruction of chlorine and the possible CC. Just a guess on my part.

Richard