Very High Ta But Everything Else Normal!

[gary3029]

I have a hottub, 1000 litres and an exercise pool of 11000 litres. A couple of months ago I switched to using bleach in both and my life has been a lot easier. I check everyday so my bleach is always correct. My ph in both the pool is now between 7.2 and 7.6 and I don't have to add anything to maintain this, unike before I used bleach. My problem is a very high TA, in the region of 180 plus and this is the same for the pool and hotub. Now what I know about water chemistry you could write on a postage stamp. However I have learned that correct levels of TA helps keep PH stable, yet I don't have an issue with my PH. My water is not cloudy, in fact since switching to bleach both have looked the best they ever have been. Could it be possible to have a very high TA and a stable PH? I have tried to lower the TA down to 80-120 but cannot do it. If the PH is stable what damage to equipment will a high TA do? My reason for concern is I have just invested in a heat pump for the pool and it states TA should be 80-120. Do I need to be concerned or is it just one of those things????

Thanks

[chem geek]

Usually with a high TA and using a hypochlorite source of chlorine such as bleach, chlorinating liquid, Cal-Hypo, or lithium hypochlorite, would have a tendency for the pH to rise. If you don't see that, then the only other problem with a high TA would be if the Calcium Hardness (CH) or pH were high in which case you could get calcium carbonate scaling. Is your pool vinyl? If so, then the CH level can be lower so the higher TA won't be a problem. Also, is your hot tub connected to your pool and sharing the same water? Do you use a pool cover?

A pool cover significantly reduces the outgassing of carbon dioxide from a pool so the pH tends to be stable even when the TA is higher, at least for pools. In a hot tub with aerating jets, it's usually hard to keep the pH stable when using a hypochlorite source of chlorine. I assume you have CYA in the water in both your pool and spa, correct?

If you post a full set of water chemistry numbers: FC, CC, pH, TA, CH, CYA then we can see if there is any problem with TA. Or you can use The Pool Calculator to calculate the saturation index to see the scaling risk.

Richard

[gary3029]

Usually with a high TA and using a hypochlorite source of chlorine such as bleach, chlorinating liquid, Cal-Hypo, or lithium hypochlorite, would have a tendency for the pH to rise. If you don't see that, then the only other problem with a high TA would be if the Calcium Hardness (CH) or pH were high in which case you could get calcium carbonate scaling. Is your pool vinyl? If so, then the CH level can be lower so the higher TA won't be a problem. Also, is your hot tub connected to your pool and sharing the same water? Do you use a pool cover?

A pool cover significantly reduces the outgassing of carbon dioxide from a pool so the pH tends to be stable even when the TA is higher, at least for pools. In a hot tub with aerating jets, it's usually hard to keep the pH stable when using a hypochlorite source of chlorine. I assume you have CYA in the water in both your pool and spa, correct?

If you post a full set of water chemistry numbers: FC, CC, pH, TA, CH, CYA then we can see if there is any problem with TA. Or you can use The Pool Calculator to calculate the saturation index to see the scaling risk.

Richard

Hi

I will try and answer each point.

It would for starters appear from your reply I have got something wrong. I assumed that if I had gone down the bleach road and checked everyday and after each use I would not have to top up with CYA. As I change 50 % of the hottub water each month and also back wash the pool on a regular basis I would say there is little ot no CYA the pool or hottub. I have used up my test for CYA. Is it essential to have CYA in a pool if it is covered when not in use. I don't have a problem with losing my bleach.

The pool has a heat blanket on it plus a thicker cover which covers the pool so as to keep out any leaves etc. The hottub is of course covered.

Up untill using bleach my TA was around 80-120 but my PH was for ever falling and I had to add chemicals most days to keep it up. Since using bleach my PH is stable and the only chemical I add is to try and reduce the TA.

The hottub and pool do not share the same water.

Yes the pool is vinyl.

Pool chemicals are as follows total hardness = 50

TC = 1

FC =3

TA = 180+

PH 7.4

I am not connecting the heat pump untill I can sort out why the TA is so high or that it will not damage the unit

Thanks

gary

[chem geek]

Gary,

Thanks for the thorough response. It really helps a lot.

It is a mystery to me as to how your TA increased so much since switching to bleach. If you had a lot of evaporation and if your fill water had a reasonably high TA then that would explain it, but your use of a cover should reduce such evaporation. The only other way TA increases that much is by addition of pH Up (sodium carbonate aka washing soda) or Alkalinity Up (sodium bicarbonate aka baking soda). It does not sound like you've added either. So I'm stumped with why your TA has risen so much.

Given the fact that your pool is vinyl and that your CH is low at 50, you do not have any problem with risking scaling so do not need to worry about that.

As far as CYA is concerned, it does have to be replaced if you remove it via dilution from backwashing or from splash-out or water change. I doubt you got it down to zero as it would take many full water replacements to accomplish that with the pool, though 50% water replacement in the spa would reduce it by half each month so 25% after two months 12.5% after three months, etc. To replenish the CYA in the pool you can add some pure CYA via the skimmer and then do not backwash for up to a week (it takes time for the CYA to fully dissolve in the filter) and keeping the pump running helps dissolve it faster. Another alternative is to go back to using Trichlor tabs/pucks for a while until the CYA gets back up. For every 10 ppm FC added by Trichlor, it increases CYA by 6 ppm. For the spa, and even for the pool, you can use Dichlor to add to the CYA by using Dichlor as your source of chlorine for a while. For every 10 ppm FC added by Dichlor, it increases CYA by 9 ppm.

Yes, you need some CYA in the water to prevent chlorine from breaking down too rapidly in sunlight. A level of 20-30 ppm should be fine if you keep the cover on most of the time; otherwise 30-50 ppm for the pool would be better (for the spa, 20 ppm should still be fine as it is covered more often).

As for reducing the TA in the pool, you can follow the procedure described in this post or this post, though as I said it's not a problem in your pool so you don't have to lower it until you get to a point where you notice rising pH or the TA gets very very high above 200 ppm. High TA will not damage your heat pump because your CH is low. It's the combination of high TA, CH and/or pH in combination that cause scaling and would be a problem. Nevertheless, if you would feel more comfortable, or to avoid any issues of voiding a warranty, you can certainly follow the procedure to lower the TA. You say you've tried lowering the TA, but I'm not sure if you followed the procedure which has you lower the pH significantly (to 7.0 or 7.2) and aerate while adding acid to keep the pH low. If you've only tried just adding acid, then that won't work, and if you've added acid and then pH Up to get the pH back up, then that will actually increase your TA.

I am very surprised that your TA is also high in your spa since the aeration and acid addition there should be lowering it over time. I assume that though your pool's pH is stable, that your spa has more of a rising pH. If it does not, then either you don't have much aeration in the spa or it doesn't get used often (i.e. every day or so).

Richard