Help...ph And Ta Very Low

[markley]

So I have recently switched to the low chlorine Nature2 system in our 240 gal tub. I am adding 1 tbsp of chlorine once a week and MPS after each soak. When I first switched to this system about a month ago, my levels were as follows (using taylor test kit):

FC = 0.4 ppm

CC = 0.6 ppm

pH = 7.8

TA = 80-90 ppm

Calcium Hardness = 150 ppm

CYA = <30ppm (filled all the way up and dot finally disappeared)

I must admit that over the last week or so I have not been checking levels as they seemed to be doing fine for the first two weeks. Anyway, I just re-tested the water and here are the numbers:

FC = 3.5 ppm

CC = 1 ppm

pH = <7 (was way low!! had to add 15 drops of the R-006 just to get it at a reasonable number of ~7)

TA = 10 ppm

Calcium Hardness = 160 ppm

I am not sure how long the pH and TA have been that low (maybe 2 weeks; do you think any damage could have been done?). Also, what could have caused this drop? the MPS? Should I add ph increaser, or TA increaser? Thanks in advance for any suggestions!!

[chem geek]

The drop in pH and TA was due to both the Dichlor chlorine and the MPS. If you are going to be using only these products (with Nature2), then I suggest you keep the TA higher and test the pH at least weekly (if not twice a week), but you'll need to watch that the CH and pH don't get too high or else you can get scaling. You can use The Pool Calculator to make sure the saturation index doesn't get above 0. Be sure to enter in the hotter spa temperature in the calculator.

The two tablespoons of Dichlor over the 2 weeks lowered the TA by around 6 ppm. 14 tablespoons of MPS, assuming soaking once every day, would have lowered the TA by around 55 ppm. So the net TA drop would be around 61 ppm which is a little less than you saw, but is reasonable since perhaps the MPS you were using was a little more acidic than my assumption (it varies by specific brand).

I calculate that the pH in the above scenario would have dropped to 5.7. Not good, but just get the pH back up quickly by adding some pH Up (or Spa Up -- sodium carbonate). I calculate that adding 3 ounces volume (6 tablespoons) will get your TA up to 126 ppm and your pH to around 7.0 at which point you can aerate the water to get the pH up further to no more than 7.5.

You might also consider getting a brand of MPS that isn't as acidic and is designated to be more pH balanced (they are all acidic, but vary in how much).

[markley]

Thanks so much!! You are always so helpful, and quick to respond! Your expertise is very much appreciated! Do you know of a brand of MPS that is not as acidic? I have been using Leisure Time with 32.18% MPS.

[chem geek]

I don't, but I'm sure some others will be able to help you out. Worst case, you'll just keep the TA higher which will help keep the pH from falling as fast and you'll periodically add baking soda to keep the TA up as it will still drop over time.

[Mikey_in_NY]

Thanks so much!! You are always so helpful, and quick to respond! Your expertise is very much appreciated! Do you know of a brand of MPS that is not as acidic? I have been using Leisure Time with 32.18% MPS.

I shock with Leisure Time (Renew) MPS only once per week, and usually notice a drop in PH of around 0.1 After every use (most days) I just add Chlorox.