CYA going down and pH going up...

[gmor]

I'm having trouble keeping my CYA levels up and my pH down. And want to know best way to add muriatic acid (see end of post).

I'm losing about 3ppm chlorine daily and would like to get my CYA up to at least 40-45 to sunscreen a bit more. I'm in southern CA and it's hot and sunny. On 6/7 I threw a couple of trichlor pucks in the feeder (and 2 more again today, ones from 6/7 are about half dissolved)) to try to keep my pH down and bring the CYA up. Not planning on using the pucks forever, but I have a few more left so figured I'd use them since I can benefit from their side effects.

I added muriatic on 6/15 and had pH at 7.3-7.4.

Im testing daily and my pH literally went from 7.5 on 6/18 Saturday to 8.2 on 6/19 Sunday so last night I added Chlorine and Muriatic and here were my numbers today:

Water Temp:80 Air temp high forecast 111 deg
pH: 7.5
FC full test = 7ppm CC=0
CH= 250
TA= 100
CYA = 25
CYA on 6/14 was 40. 6/5 was 35. 5/30 was 42.

I added water on 6/12 (filled for 2 hours)and last night 6/19 (filled for about 45 mins- maybe 1.5 inches filled) Does that account for the CYA loss?

And one last random question... Is it ok to add chlorine and muriatic acid in the same "session" or do I have to wait after adding one before adding the other. I usually walk chemicals around the pool when adding, but heard there is a difference between walking muriatic and adding to one spot by a return? Ok that's 2 more questions. ?
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15000 gal in ground plaster pool (original late 60's plaster), Pentair FNS plus 48 sq ft DE filter, Pentair 1HP 1.65 sq ft pump. No heater. No pool sweep (yet! Any advice on a lesser expensive one?)

 

[jagger2005]

Welcome to TFP.

Water loss to evaporation will not cause CYA or any minerals (Calcium, Salt, etc) to lower. They stay behind when the water evaporates. Are you getting your test results from a test kit or a pool store? The 3 readings you posted are so close, the difference is probably insignificant.

I add muriatic acid in front of one return. IMO, the less movement the better. MA can be dangerous if improperly handled.

And it is my understanding that you should not add chlorine and MA at the same time. I think you should at least wait 30 minutes. Some one will correct me on this if I am wrong.

 

[jagger2005]

If you pH moves from 7.5 to 8.2 in one day that is pretty aggressive movement. Since you lowered it back to 7.5, check it again tonight and see what it is and adjust accordingly. If it is back up to 8.2, I would try to adjust down to 7.2 - 7.4. Eventually, the rising pH will slow down.

 

[gmor]

I'm doing all my own testing and being as consistent as I can. I'm just surprised to see the CYA going down not up since I've got the tablets in. What I meant about evaporation was that maybe the CYA lowered when I refilled? Anyways I tested pH today just now and it's at 7.5 so creeping up but not as fast as the past couple days. I'll keep lowering it and hopefully can get it stabilized.

 

[duraleigh]

You are not using enough tabs to be really effective (look at the bottom of PoolMath if you want to calculate it. By far, the best bet is to by enough CYA to bring your pool to a total of 50 ppm, put it in, and you are done with it. You will go the rest of the summer messing with the tabs.

That said, the tabs are helping (a little) keep your pH down so the call is yours to make.

 

[triptyx]

I'm doing all my own testing and being as consistent as I can. I'm just surprised to see the CYA going down not up since I've got the tablets in. What I meant about evaporation was that maybe the CYA lowered when I refilled? Anyways I tested pH today just now and it's at 7.5 so creeping up but not as fast as the past couple days. I'll keep lowering it and hopefully can get it stabilized.

Evaporation "purifies" the water. What leaves the pool in vapor form is basically nearly pure water. As stated above, the CYA, minerals, salt, and other compounds that are suspended in the water are left behind - concentrating CYA, minerals, salts, etc. When you replace the evaporated water with fresh water, you're just re-diluting the existing CYA, minerals, etc, and possibly adding more salt and minerals depending on what is in your fill water. The only "easy" way to reduce calcium, salt, and CYA is to physically remove water from the pool (pump it out, splash it out, backwash, etc) - thereby removing those suspended compounds from the pool completely, replacing the removed water with water that has lower concentrations of those compounds.

 

[gmor]

Thanks... I'll buy some CYA and just bring it up quickly. Thx.