New house, new pool

[muttley]

I am maintaining my own small (30 m3) pool with great help from this website. Not had a pool before, but at 72 never too old to learn something new. Last year (year one for me) fitted new pumps, non-return valves, sand filter and purchased a pool cover to help with heating in summer. Also did some tilework and re-grouted the pool which gave me a chance to refill it with clean water and start chemicals from scratch (CYA was off the scale after fifteen years of tri-chlor tablets). As expected, the new tile grouting had an effect on the pH and I have been adding pH- regularly. Also last summer, in an attempt to manage CYA I started adding liquid chlorine which has a relatively high pH. Over the past winter the pool has been covered so chlorine demand has been negligible but pH is still going up (from 7.5 to over 8 in a week), plus it is now a year since the pool was grouted. I live in southern Portugal so winters are not a big issue and there are plenty of blue skies, just too cold for me to be swimming.
A few houses nearby have identical pools and mine is the only one with a pool cover on almost permanently. They don't seem to have the same pH issues. So two weeks ago I removed the pool cover and guess what.... my pH hasn't changed at all. Does anyone know what is going on? It's a small infinity pool but there are no problems running the pump with the cover in place.

 

[mknauss]

What is your TA? Elevated TA can make your pH rise quicker.

Do you add fill water to make up for evaporation? The TA of your fill water will also push your pH up.

 

[muttley]

Thanks. TA is around 90. It hasn't moved much. At the moment we don't need fill water. The infinity tank provides a reasonable buffer. When it does rain it can sometimes overflow this. So rainwater is the biggest influence at this time of the year. I needed to add some alk+ after a rainstorm a few weeks ago.

Thanks again
Martyn

 

[mknauss]

With that elevated TA your pH will rise.

Keep the pH in the 7's. Let the TA fall. As long as it does not go below 50 ppm or so, all is good.

 

[muttley]

OK will do. What should TA be ideally. I see different figures quoted in different places. What is interesting though is that as soon as I left the pool cover off, the pH stayed constant. Next time we get some heavy rain I plan to check the rainwater pH and TA and hardness.
Thanks
Martyn

 

[mknauss]

TA is whatever, at or above 50 ppm, that keeps your pH as steady as it can be.

Rainwater is normally pretty acidic but has no TA. Rain hitting the surface of a pool will drive up pH as it is aerating the water.

 

[muttley]

Thanks