Water check!

[acroy]

This is a 33k in ground gunite SWG pool

CL 4
PH 7.7
TA 40
CH 550
CYA 30
SALT 4000
Borates 30

CH – at what point ‘must’ the water be replaced to reduce CH? 750? 1000? Incoming water is 120ppm, it is no minor expense and hassle to drain the pool 2/3 and refill, dosing up salt, cya, borates, acid.

TA – 40 seems kinda low. pH is adjusted with liquid acid every 2-3 days. Pool started @ TA 150 a couple years ago and has been falling since. Is 40 OK?

CYA – low for my area, waiting to dose it up till I decide to replace the water now or later.

Overall – pool looks good, feels great, no CH build-up on tiles or SWG cell.

 

[yeggim]

I wouldn't worry about those CH numbers. It's true that the only way to lower CH is draining and refilling but if you're replacing water from splash out and backwashing with fill water of 120 CH, you should not have a problem. Of course evaporation doesn't count. In that case you're just adding 120 CH to the water. Rainfall will dilute CH but not if it's just replacing evaporative loss. Do you close for the winter?

Now is a perfect opportunity to get your CYA and Borates adjusted.

Before doing anything, I would raise TA to 60. What do you use for Borates.

 

[duraleigh]

What do you use for Borates.

Just a general note....borates are not in any way necessary for a pristine pool

1. Keep your pH below 7.5 and your Ch will not be a problem

2. raise your TA up to 60 - 80 using baking soda

3. Adjust CYA when you get ready.

 

[acroy]

- rising CH is from heavy evap - hot windy day like today costs 1/4" of water or more. CH creeps up pretty quick generally May-Oct
- Using borax+acid for borates. I know it's not necessary but does give a nice shine, feel, and I understand it's minor insurance against algae as well.
- pH under 7.5 makes the CSI very negative according to the pool calc - I try to keep it around -.2 or -.3, is this not right?

 

[jblizzle]

If you also raise the TA, the CSI will not be so negative ... although this makes clear that you are paying attention and pretty well aware of your pool's chemistry

 

[acroy]

Thanks for the input - Can anyone confirm it's OK to run the CSI heavily into the negative range? I want to maintain the plaster in excellent condition as long as I possibly can!

 

[yeggim]

Thanks for the input - Can anyone confirm it's OK to run the CSI heavily into the negative range? I want to maintain the plaster in excellent condition as long as I possibly can!

Here's an excerpt from PoolCalc:

CSI - Calcite Saturation Index

The calcite saturation index is a tool for estimating the likelihood of plaster corrosion or calcite scaling. The LSI, Langelier Saturation Index, is a very similar but slightly less accurate measure. The CSI uses pH, TA, CH, CYA, temperature, Borate, and Salt levels to estimate the likelihood of problems. A low saturation index means the water is likely to dissolve calcite out of plaster, pebble, tile, stone, and concrete surfaces (and perhaps fiberglass) which will eventually cause damage. A high saturation index means the water is likely to deposit calcite scale on the walls of the pool and in the plumbing.

CSI is most sensitive to changes in pH. With a plaster pool, it is best to try and get your CSI a little below zero, so that changes in pH won't shift your pool too far towards corrosion or scaling. With a vinyl pool the CSI can be kept more negative, which makes it very unlikely that pH changes could get the CSI into the range of scaling risk.

 

[acroy]

OK, I was focusing on pH only: with the current chemistry, running pH 7.4 makes CSI -.53, which scares me.

Adjusting TA to 80 and CYA to 80 brings it back to -.24, more reasonable. whew. Thanks for inputs.

 

[yeggim]

OK, I was focusing on pH only: with the current chemistry, running pH 7.4 makes CSI -.53, which scares me.

Adjusting TA to 80 and CYA to 80 brings it back to -.24, more reasonable. whew. Thanks for inputs.

Good move on the TA. Adding another 50 ppm of CYA should knock your TA down a bit and will lower your Ph. That should allow you to sneak a bit of your Borates in without having to add Muriatic acid.

I did Borates last year and was quite pleased with the results. PH was rock steady and I notice a slight increase in Chlorine this year from last year. Last year we had a half years average precipitation fall in a month. Between over two foot of rain and winterizing, my borates don't even register this year.