pH rise only at high output?

[geko29]

For about a month, my SWG kept my FC constant at a setting of 3/8, running for 4 hrs/day, with the cover on. On the weekends we left the cover off, and I turned it up to 4/8 and an 8 hour runtime to achieve the same result. Throughout this entire time, pH remained rock-steady at 7.6.

However, with as hot as it's been this week, I've left the cover off all week so I can swim after work. Not wanting to run the pump 8 hours every day, on Tuesday I changed it to 4 hours/day with the SWG at maximum output. FC output is basically keeping up with loss. But my next pH test was 7.8, and the next one after that was 8.0. I added some Muriatic acid this morning to bring it back down.

But it seems strange that pH would not rise at all when running the SWG at low output for weeks on end, but then a few days turned up all the way and it spikes rapidly. Does this seem logical to anyone?

 

[Richard320]

With the cover off, you probably started losing more water to evaporation than before and had to top off. What's your fill water like? Ever tested it? If it's high in TA and/or pH, that could do it. My pH stays pretty steady until I add more water, then i have to add acid.

Also more swimmers = more aeration = pH rise.

 

[JamesW]

The cover holds in carbon dioxide. With the cover off, the carbon dioxide gets out and the pH rises.

 

[geko29]

With the cover off, you probably started losing more water to evaporation than before and had to top off. What's your fill water like? Ever tested it? If it's high in TA and/or pH, that could do it. My pH stays pretty steady until I add more water, then i have to add acid.

Also more swimmers = more aeration = pH rise.

No, the pool was full up to the top mark on the skimmer due to some heavy rains, and we got a little more rain. I’ve only added fill water once this season, maybe 5-6 weeks ago? TA fell from 70 to 60 over the last two weeks, so I don’t think that’s the culprit.

The “bather load” is comprised of me going in there 3 days after work for 60-90 minutes, standing by the side with a drink in one hand and responding to emails on my phone with the other.

 

[geko29]

The cover holds in carbon dioxide. With the cover off, the carbon dioxide gets out and the pH rises.

Definitely a possibility, I did not know that.