CH rising?

[DONNIE]

I think I have been trying too hard to keep the Ph at 7.5 so every other day when it hits 7.6 I add the 7oz of acid. Last week I wanted to see how high it would go left unadjusted. To my suprise it has remained stable at 7.6 and I haven't had to add any all week. I'll retest the Ch tonight at room temp. Thanks for your advice.

Donnie

[chem geek]

A change in pH from 7.5 to 7.7 might cut down your rate of CO2 outgassing by almost half and cut the acid demand in half, but a change from 7.5 to 7.6 shouldn't be so dramatic as having virtually no pH rise in a week. I'm sure something else has happened coincidentally (maybe something simple like there is less wind). At any rate, the point is that you can live with a higher pH and this will have you add less acid and that is what you are seeing (albeit more extreme than expected).

Richard

[DONNIE]

Can you actually "smell" out-gassing? thought I could smell my pool the other night for the first time.

[chem geek]

Carbon dioxide is odorless so you can't smell it. If you are smelling chlorine, then that is possible (a "clean" chlorine smell unless you have combined chlorine), but I'm not sure why you'd be smelling that now all of a sudden.

Richard

[DONNIE]

Im not even sure it was my pool. Zero CC's. It's been really wet and cold here so Im sure it was just the weather. That or the Opossum thats been hanging around.

Donnie

[CarlD]

I, on the other hand, am baffled by the rising calcium hardness. Nothing you are doing should cause that.

So...Next question: Is your waterfall fiberglass, too, or is it stone and even mortered?

[chem geek]

Carl,

That's an excellent question (and I, too, look forward to hearing the answer) because normally the slightly corrosive water wouldn't be expected to dissolve calcium carbonate, but perhaps the extra physical erosion of a waterfall might accelerate that process. The problem is that the amount of calcium rise he is seeing is inconsistent with the amount of carbonate that must also be introduced and this should increase the TA and pH and require a lot more acid than is being added to have his TA actually drop from 80 to 70.

If I use the pool numbers given, then adding 7 ounces every other day for for 19 days is 8.3125 cups of 31.45% Muriatic Acid. I can then reproduce maintaining a pH of 7.6 and having the TA drop from 80 to 70 if I assume corrosion of calcium carbonate of 18.9 ppm and a large outgassing of carbon dioxide.

So SOME increase in calcium of around 20 ppm can be explained through corrosion, but not an increase of 70 ppm unless there is some strong acid somehow getting added to the pool (which I doubt -- beyond the Muriatic Acid, of course). I'm betting that the calcium test is off a bit, possibly due to temperature dependence and I'll be eager to see his new measurements.

Richard