Ta And Ph With Aeration

[Stringy]

I have a basic 300 gallon spa (Sundance Hermosa), and have been using bromine tabs. I've read the Bromine for Beginners thread (and quite a few others) which have been very helpful.

I've been fairly successful keeping the water chemistry in check, except that when I set the TA to 50, the pH keeps rising until the TA is used up, even if I also use borax. I believe my spa has a simple pump setup such that whenever the pumps are running to heat or filter the water, the water goes through the jets, i.e. aerating. From reading the "Ta Low And Ph High...please Help!" thread, I'm wondering if the aeration would cause the rising pH.

Does this sound likely? Suggestions? I don't even care about the jets having bubbles. Could I block the air intake somewhere to stop the aeration?

[chem geek]

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The TA is getting used up because bromine tabs are net acidic. If you used sodium bromide and oxidized it using bleach, then the TA would likely remain more stable but you'd have to add the oxidizer regularly to make more bromine (that's why tabs are more convenient if you aren't using the spa regularly). If you use non-chlorine shock (MPS) for oxidizing to produce bromine, then that is acidic. If you use Dichlor for oxidizing then that too is net acidic. Such acids will deplete the TA over time.

Aeration most definitely causes the pH to rise because aeration increases the rate of carbon dioxide outgassing. You can minimize this by keeping the TA low (around 50 ppm), targeting a higher pH (don't add acid until the pH gets to at least 7.8 and don't lower the pH below 7.5), use 50 ppm Borates, and try to minimize the amount of aeration (if possible, have the circulation pump not use the jets, though it sounds like it doesn't work that way in your spa).

Blocking the air intake should help reduce aeration, but someone else will have to help you with how to do that.