Question about SWG target levels and CSI

Jump to latest Follow Reply
T

toddb

0
Jan 12, 2014
8
Chandler, AZ
I became a pool owner a couple of weeks ago and I've been learning, testing, balancing and everything seems to be going well. The salt cell was very scaled so I cleaned it (with guidance from TFP.com) and over the past few days FC jumped to 6.5. I've reduced the pump run time and SWG % to let it come back down to the 3-4 range. I've been using Pool Math but hadn't looked at CSI until today. Right now my levels are:
FC 6.5
CC 0
CH 200
Ph 7.8
TA 130
CYA 30
Salt 3700

I haven't tested for borates but entered 0 in pool math. Water temp is 52F. According to pool math my CSI is -0.2 and it says that is balanced. So far so good. When I enter target levels that I got from the Water Balance for SWG page in Pool School:
FC 4
CH 250 (I've been told CH will rise some due to evaporation)
PH 7.6
TA 80
CYA 70
And add current salt, borates and temp
Salt 3700
Borates 0
Temp 52F

Pool Math says my CSI will be -0.71 and it says corrosion of plaster likely.

I'm not trying to get my TA down to 80. However, I have noticed that I have to add acid to lower the pH about every other day and that wasn't happening as often before I took over the pool so I assume with more consistent dosing of acid the TA may drift down some over time. Assuming TA will drift down to 110 and pH will usually be around 7.6 pool math says my CSI will be -0.42 and it says that has the potential to be corrosive to plaster.

My questions is, should I be concerned? If so what target levels should be adjusted?
 
First, don't target 3-4 for your FC. I target 6 because it is very easy to slip under the minimum FC if you START at the minimum. Make sense? When I was having a few issues, my FC was only holding around 3-4 and I was getting black algae in the grout at the water line, and anywhere the plaster was rough. So, bump that up to 5-6 and keep it safe. At FC of 3, your surface water will be under 3. Danger, Will Robinson! :)

Zero for borates is correct. Don't bother messing with measuring if you haven't added them.

CH won't rise just due to evaporation. It will rise if you have evaporation and add fill water with CH. The amount of rise depends on the CH in the fill water. This may be minimized or eliminated if you have a sand or DE filter, backwashing pulls pool water out and gives you the opportunity for fresh water. If your fill water is low CH, this is a good thing.

It is very common to have to add acid with a SWG. I don't know where I will be now that I've remodeled the pool, but last year I added about a gallon a week. Keep in mind that I have a very large pool, and was required to run the SWG at 100% for most the summer due to a black algae issue (see above), which was a real problem due to my bad plaster. Now I have all new pool surface and I expect to be able to run at a lower percentage and run time this year. I'm currently at 30% for only a few hours, but the water is still cold.

That all said, with TA at 130, you will have more pH drift than you would if you would get your TA down to 70. It should be a goal for you. Every time you add acid, target 7.2 and it will come down over time.

I would get that CH up over 250 ASAP.

I know I haven't gone into your CSI number, but I feel the pH, TA, and CH are a bigger concern for you at the moment.
 
Hello,
With your TA that high PH climbing is going to happen. I added CH to my pool to offset the low CSI in my pool. I've got a 17K pool (see signature for details.)

If you play with poolmath (http://www.troublefreepool.com/calc.html) you'll get an idea of what you'll need to do to get a more neutral CSI. I like to run a slightly negative CSI it keeps scaling in the cell down.
 
The main thing is to allow the PH (or TA) to go a little bit higher than normal while the water is cold (which it will tend to do on it's own). Then, when the water warms up you can bring the PH and/or TA back down to recommended levels and you will be just fine with CSI around -0.4.
 
Thanks for the quick responses. I played with the numbers some more and I see what a difference temperature makes. I won't worry about the TA for now and I'll watch CH as we get into summer and expect that it will climb then. With a CH of 200 does it make sense to raise it a little now or let that happen on its own? If I increase CH now do I do that by adding Calcium Chloride?

Thanks so much for the help!
 
That depends on your fill water CH level. Living in AZ yours is probably high, but there is high and then there is really really high. The higher the fill water CH level the more trouble it is worth to keep CH as low as possible, even if that means raising TA for now and lowering it later.

If you do want to raise CH, calcium chloride is the obvious choice. In many areas you need to purchase it from a pool store, but sometimes you can find it in big box hardware stores, either as an ice melter or as a concrete curing accelerant.
 
Thanks Jason. The hardness of my fill water has had me confused. It tests at 200, same as the pool. I was expecting it to be much higher than that. I did some reading on the city water department web site and they say the hardness here varies between 5-20 grains per gallon with an average of 16.5. 1 gpg = 17.1ppm according to Wikipedia so that would translate to roughly 86 - 342ppm with an average of 282. So my water is testing close to their average. Given that I think I will raise it some targeting 250 and then keep an eye on it over the summer.

Thanks again for all of the help. This site is awesome!
 
That CH will come up on it's own this summer I promise you. If it were me, I'd let it cycle up naturally if I were at 200.

Oh how I would love to be where you are with that CH level. Instead, I'll have to opposite problem.
 
This link says that Chandler's water hardness is 5-20 grains/gallon with an average of 16.5 as you noted. This is 282 ppm, but this is Total Hardness, not Calcium Hardness. That is, Total Hardness includes the hardness from magnesium as well as calcium. Usually, there's more calcium than magnesium and with typical ratios your CH of the fill water may be around 200 ppm and that's what you reported so that's consistent.

The CH of your pool should rise with evaporation and refill. Water dilution when refiling with fill water won't lower your CH in your case. Dilution from rain will.
 

Enjoying this content?

Support TFP with a donation.

Give Support
It's kinda off topic but I noticed your pool size is 9100 gallons estimated. If/when you use poolmath to compute the chemicals to use, and if it over or undershoots your values it can give an indication if you're over or under in your pool size value. But aren't all pool sizes really just an estimate due to a couple inches in fluctuation. :)
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply