CSI during shoulder seasons - alter chemistry to avoid corrosion?

[thejeff]

Hi all,

My first year with a pool. I currently have my chemicals dialed in with my CSI around -0.28, which I understand we want it higher than -0.3. In order to get to a non-corrosive CSI, my chemicals are at the top of their ranges (CH at 320, TA at 80) with water temperature above 85F.

My problem is during the shoulder seasons when I don't want to heat the pool but want to keep it chlorinated and circulating. Water temp in the 60's (which is what I would get during those periods without the heater running) brings my CSI around -0.50 ish which PoolMath tells me I should avoid having for prolonged periods of time.

How big of a deal is this? I really want to avoid premature corrosion of my equipment so am curious on your thoughts.

My pool is fiberglass with concrete paver coping around it. There is no metal in the pool - only metal contact I can see is the pool pump and the heat pump. The heat pump would be bypassed during the shoulder season, however.

pH 7.4
FC 6.0
TA 80
CH 320
CYA 70
Salt 1700
Borates 35
Temp 86

Adding more Calcium would help to bring the CSI in check with lower water temperatures but it would bring me over the recommended range...

Thanks!

 

[Leebo]

Rather than adding calcium I'd let your pH go up instead as that's easier to adjust up and down as the water warms up or cools off.

 

[thejeff]

Rather than adding calcium I'd let your pH go up instead as that's easier to adjust up and down as the water warms up or cools off.

Thanks - just tried in Poolmath and I guess I didn't realize how big of an impact pH had on CSI. So if in the shoulder season and nobody is swimming, running pH at 7.8 or so is acceptable and will have no adverse affect?

 

[Leebo]

pH is actually one of the largest “players” in CSI which is nice as it’s one that the pool owner often is able to manipulate the most. Some find maintaining a higher pH is actually a good thing. The amount of time it takes a pH of 7.4 to increase to 7.6 is faster than the amount of time it takes to increase from 7.6 to 7.8. Generally speaking, the higher the pH, the slower the increase.