My CSI is -0.62, but my numbers are near perfect, what gives?

[ajdevp]

Hello,

Just did my numbers with Taylor K-2006 FAS-DPD chlorine kit, they are:
FC = 5.4
CC = 0
PH = 7.2
TA = 80
CH = 260
CYA 42
CSI = -0.62

Why is my CSI bordering on corrosion? I have plaster, concrete gunite pool, and my plaster is already sharp with little crystals that cut the skin.

Appreciate any inside knowledge on this, I'm very vigilant checking my water chemistry. I owe it all to Trouble Free Pool, you guys are great.

Thank you,
Adrian

 

[mknauss]

ph and CH are on the low end of the acceptable range and I suspect the water temperature you have entered is pretty low?

Let the pH rise (it should on its own with a TA of 80) and the CSI will be fine. Add some calcium if you wish. Higher water temperature will raise the CSI too.

 

[CrystalRiver]

That CYA result didn't come from a Taylor kit. Taylor only gives readings in multiples of 10.

In short, your pH is at the low end, your CH isn't high, and your TA is not high. CSI is a formula that uses all of those data points, and a few more, but those three are the major contributors. With several numbers at the lower end of acceptable, the CSI is too low.

Play around with Pool Math and see how changing those numbers changes CSI. For now, I suggest raising pH, since it's the quickest and easiest to change and also very reversible. One calcium is added to the water, it only leaves when liquid water leaves the pool, so I'm slower to recommend adding that.

 

[ajdevp]

Crystal River, you're right the Taylor Kit shows CYA in multiples of ten, but when you stop seeing the black dot, the water level doesn't always land on that multiple of ten, so you have to estimate what the number is, that's what I do.

Since, we're talking about the Taylor Kit, what is your advice on the determining the CH accurately. My water turns lavender/purple before it turns blue as I add the drops. Purple isn't blue. How do you guys recommend I stop counting drops, when it's light blue, deep blue, or when it turns lavender/purple? Thank you.

Adrian

 

[Texas Splash]

the Taylor Kit shows CYA in multiples of ten, but when you stop seeing the black dot, the water level doesn't always land on that multiple of ten, so you have to estimate what the number is, that's what I do.

We generally recommend just rounding up or down.

My water turns lavender/purple before it turns blue as I add the drops.

Keep going until you get to the light baby blue. That's the final CH number.

 

[Kellyp]

If I'm not sure that I'm at the end color, I add one more drop. If no change I'm done and I subtract the drop that made no change. If any change, deepening of color, brightening of color, I add another till no change detected. Always subtract the drop that made no change from your total drops counted.

This tip courtesy of mknauss, thank you sir, works every time I'm unsure.