Effects of auto cover on water chemistry

[nawp]

I've tried scouring for all the answers I could find about how a pool cover would affect chemistry but still have a few lingering questions. It seems that a cover will generally reduce FC loss from UV. Additionally, it should slow pH rise since it cannot off gas CO2. Both of these things sound good, but what happens if the cover is on for a good period of time? What happens to the trapped CC if you don't allow it to breathe regularly? What happens if the CO2 is trapped for a long period of time?

I'm mostly asking because prior to converting to TFP, I recall PB telling me that the cover was causing issues with the chemistry. So, we would always leave it a few inches open to allow it to off gas.

IIRC, the issue we were having was spikes in pH, but this seems contrary to what I've read on this forum. Was PB just flat out wrong?

 

[mknauss]

You really should open the cover every few days to allow the sun to shine on the pool surface. That will allow the CC to be eliminated and also let some CO2 off gas.
Typically, a covered pool will see declining pH due to CO2 build up in the water. No idea why your pH would increase. Of course pH would increase when the plaster was new.

 

[nawp]

You really should open the cover every few days to allow the sun to shine on the pool surface. That will allow the CC to be eliminated and also let some CO2 off gas.
Typically, a covered pool will see declining pH due to CO2 build up in the water. No idea why your pH would increase. Of course pH would increase when the plaster was new.

Ok. It was rather new plaster (~1 year old) when this was happening. So perhaps that was it.

In theory, what can happen if you don't allow the CC and CO2 to off gas?

 

[mknauss]

The CC can impact the cover longevity. It will also stink when you open it. pH can drop low but doubt it will drop to damaging levels. Might irritate eyes and skin.