Low CH but CSI in range ... dangerous for plaster in rough shape?

[cbredesen]

Hi folks,

My water looks amazing now thanks to what I have learned here. Today's readings just before adding liquid Cl:

FC 5.5
pH 7.8
TA 90
CH 150
CYA 45 (after *four* water replacements, ugh!)

So my CSI according to poolMath is around 0.09 which is in range. But CH seems like it shouldn't be @ 150 like mine. Now, my diamond brite (or whatever it is) is in terrible shape, coming off and every time I clean my cartridge it's full of "diamonds". We know it needs to be redone but we're not quite ready yet. My question is ... with the surface in bad shape, should I go higher on CH to protect it till we can refinish or what?

 

[Casey]

Welcome to TFP.

You should add some Calcium to your pool. Also, your pH is on the high side. That needs to come down before you add it to the pool or you'll make it cloudy.

Check out Pool School and read the ABC's of pool water in my signature link to get a feel on what you should be doing to take care of *your* pool.

 

[wjr75]

I think you want your calcium at around 250 otherwise it will suck it out of your plaster. I have a newer finish last year and I add it in the spring to bring it up. My fill water every spring is only 150.

 

[cbredesen]

Thanks guys ... I'll get it straightened out this weekend!

 

[jblizzle]

If you were in Arizona or Texas I would tell you to leave it since the CH will rise over time just due to evaporation. But being in Florida with the rain you get you probably are gonna have to bring it up to be safer.

 

[PAGirl]

I am thinking .06 is the upper range for CSI.

CSI Calcite Saturation Index - requires pH, TA, CH, CYA, Temp, uses Borate, Salt
Less than -0.6 is suggestive of problems for plaster, tile, stone, and pebble pools.
Greater than 0.6 is suggestive of problems for all pools.
From the bottom of the pool calculator.....

 

[chem geek]

+0.06 is fine; It's +0.6 that is close to when we see calcium carbonate scaling in some pools.

Actually so long as the pH stays at 7.8 there's nothing wrong with the CH at 150 ppm. The main risk of a higher pH is staining from metals, but if there aren't metals in the water then it's not a problem. It's up to you and I wouldn't sweat it either way. pH 7.8 and CH 150 or raise the CH and have the pH target be lower. If your pH tends to rise, then having the higher pH target may be a better sweet spot for a slower rise in pH.

Remember that it isn't calcium by itself that gets dissolved from pool plaster but calcium carbonate. Carbonate is in TA and at higher pH there is more of it so having a lower calcium and a higher carbonate can still saturate the water to help prevent dissolving of plaster.

 

[cbredesen]

+0.06 is fine; It's +0.6 that is close to when we see calcium carbonate scaling in some pools.

Actually so long as the pH stays at 7.8 there's nothing wrong with the CH at 150 ppm. The main risk of a higher pH is staining from metals, but if there aren't metals in the water then it's not a problem. It's up to you and I wouldn't sweat it either way. pH 7.8 and CH 150 or raise the CH and have the pH target be lower. If your pH tends to rise, then having the higher pH target may be a better sweet spot for a slower rise in pH.

Remember that it isn't calcium by itself that gets dissolved from pool plaster but calcium carbonate. Carbonate is in TA and at higher pH there is more of it so having a lower calcium and a higher carbonate can still saturate the water to help prevent dissolving of plaster.

I just now saw this after I had added some Calcium, bringing my CH to around 270. I did drop pH to 7.5 before doing so but now it's up to 8.0+ ... is it normal for the pH to raise when you add Calcium?

 

[jblizzle]

Adding CH should not really raise the pH. Lower the pH back down.

Aeration from waterfalls, spa, etc can raise the pH.