"Balanced" Outside PoolMath Goals

[johnsimion]

My questions primarily concern the "goals" on PoolMath. I seem to consistently get "balanced" results on the CSI using PoolMath, even though I'm pretty far outside the "goals" it shows for me.

Since I last posted here, I had to drain and refill again, and this time the pool is filled with almost entirely soft water. Today's readings (Taylor except as noted):
FC: 21 (FAS/DPD)
PH: 8.2
TA: 130
CH: 200
CYA: 33 (this is hard to read -- ColorQ says 31)
Salt: 3000 ppm
CSI: 0.26 balanced

Question 1: How high MUST I get my CYA? The Pool School doesn't even list any figure lower than 60 for CYA in a SWG pool, and PoolMath says it should be 70. Is there any actual harm if my CYA is 32, as long as there is adequate chlorine in the pool? Right now I have excessive FC because I've been both running my SWG and putting leftover CYA tablets, er, I mean trichlor tablets, into my skimmer in order to get my CYA up (I have about 30 lbs of the tablets and I figured WTH, they increased my CYA to ridiculous amounts before I had the SWG so why not). I understand this is a bad idea over the long term, but I don't plan to do this any longer than needed to get the CYA back up. I plan to turn off the SWG today, so the chlorine should return to something more normal.

Question 2 is about my CH. It is actually low; PoolMath says my minimum should be 250. I was measuring 225-250 the last couple of times I tested, which was on the low side but close. Today it really seems to be about 200. Do I need to be concerned, given that the PoolMath says I am balanced? I don't want to eat up my pool, but after the calcium buildup I've had in the past, I do want the calcium to be as low as I can safely go. If I should increase the CH, would it be okay to slowly increase the CH by simply turning off the outside softener for a while and letting the extremely hard tap water do its thing to slowly increase the CH?

Question 3: In another thread here, ChemGeek said: "The CH may continue to go down with water dilution from rains so adding more calcium would be reasonable. I do that over the winter since I'm diluting to reduce salt, but don't want the CH to get too low." I am confused. I thought that CH was like salt, that dilution would only apply if the pool overflowed or at least that the total quantity of water went up. We actually did have some rain here in Vegas in the last few days, although the quantities were pretty minimal as you might expect. Could even a small amount of rain explain why my CH test went from 225-250 down to 200 today?

Question 4: I have noticed that my PH and TA have been verrrry stable since the last refill. I last tested two weeks ago. At that time, I added 22 oz of acid two weeks ago and today's test shows the exact same readings as I had before I added the acid. In fact, they are the same readings I had a week before that. Even before the refill, I noticed that my pool really likes to have a PH of 8.2 and TA around 110-130. PoolMath says my goals should be 7.8 max for the PH and 70 minimum for the TA. I can bring my pool within those goals only with a LOT of acid, but after I do that, they go right back up to the 8.2/130 figures and then stay there. Here's the question: Given that PoolMath says my pool is balanced at 8.2/130, can I just not worry about those readings? Would they hurt someone swimming (not that anyone is swimming now)? Or, would this cause other problems in the pool?

Thanks for your help.

 

[JasonLion]

1) Low CYA with a SWG will reduce cell lifetime significantly and make the pool more prone to problems (low CYA allows FC levels to fluctuate more drastically). This is not such a big issue if the water is cold, but even then far from ideal. Trichlor tablets will raise the CYA level, but that will take months.

2) Well yes and no. You don't want PH at 8.2. The common PH test only reads up to 8.2, so your PH could be higher. You are also risking metal staining (but only if there are metals in the water). If PH really is 8.2, then CH is fine where it is for the moment. And if you have high CH fill water you don't want to manually add any CH and need to compensate other ways.

3) The CH test results are +- one drop, so variations of +-25 are normal and should be ignored. If you do get any significant rain, you would normally use that to lower the CH level over the winter by removing water and replacing it with rain water. If that is not what you are doing, then CH won't go down.

4) I suspect that your PH has only been "stable" because the test is reporting anything above 8.2 as 8.2, and actual PH is much higher. If you can confirm that PH is actually 8.2, then no big deal. More generally, you must have either high TA and/or high CH fill water, which means the rules are a little different. You may need an automatic acid feed system in the long run. Short run, which CH is very low, you are alright (as long as PH isn't much higher than you think). But as CH goes up over time you are going to need to eventually keep PH and TA lower then they are now.

Finally, with a SWG you want to keep CSI at zero or below. The CSI inside the SWG is far higher than it is in the pool. To avoid calcium scaling the SWG cell you generally need to keep CSI at zero or lower.

What are your fill water TA and CH levels?

 

[zethacat]

When you have more than 10ppm chlorine in your pool, you will get a false high reading on PH so your reading of 8.2 may be wrong. With a CYA of 30 your target FC is 6. Unless you are SLAMing for mustard algae there is no reason why you should have 21ppm chlorine in your pool. Let your FC drift down to below 10 and check your PH again. I wouldn't feel comfortable allowing it to stay at 8.2. Once it hits 8.2 that is a red flag that it's time to lower it because if it gets higher than that you won't know.

 

[chem geek]

In another thread here, ChemGeek said: "The CH may continue to go down with water dilution from rains so adding more calcium would be reasonable. I do that over the winter since I'm diluting to reduce salt, but don't want the CH to get too low." I am confused. I thought that CH was like salt, that dilution would only apply if the pool overflowed or at least that the total quantity of water went up.

The CH is like salt in that dilution only applies if the pool overflowed or the total water quantity went up. In my pool I have an explicit overflow area where the automatic pool cover is rolled up and it has a pipe to the sewer. So when there is sufficient rain, the pool overflows and EVERYTHING in the pool gets diluted or lowered since rain water doesn't have very much in it except water. So my TA, CH, CYA, and salt levels all drop. To keep things in balance, I add some CH but I usually wait to deal with the CYA in the spring since chlorine usage is so low during the winter. The primary reason I do this overflow is to keep salt levels in check since otherwise they would climb from my use of chlorinating liquid and having an oversized cartridge filter that only needs cleaning once a year (so no regular backwashing or cleaning that would dilute the pool water).

In an SWG pool, one doesn't have to worry about salt buildup since the chlorine is made from salt and when gets used up reverts back to salt. One might consider rain dilution to refresh the water since there are some types of dissolved chemicals that can build up over years, but again this depends on one's specific situation. It's more expensive to replace water in an SWG pool since you have to add significant amounts of salt.

 

[johnsimion]

What are your fill water TA and CH levels?

Fill water TA ranges from 150 to 170. The filler is attached to a water softener, so unless I bypass it, the CH going in is near nil. When I started this pool, it had the local hard water and resulted in severe calcium deposits that required bead blasting within six months -- in addition to high CYA due to using trichlor tablets -- so I bought the water softener for the fill line, and drained and refilled the pool with mostly soft water. Hence the low CH readings. However, that does nothing for the TA or PH issue. The PH is also exacerbated by the spillover for the spa ... the infloor system insists on overflowing the spa multiple times per hour, aerating the water and probably increasing the PH. In the past, I have been frustrated with the fact that I can add huge amounts of acid and get very little results from it, both in terms of PH or TA. The lowest PH or TA I ever achieved was 7.1 or so and TA of about 80, but that was after adding about three times as much acid as PoolMath said I should add to reach that PH! We're talking more than two GALLONS of acid at one time. I did that out of frustration, because adding the "right" amount of acid never has much effect. And PH and TA crept right back up there anyway. So I am starting to wonder whether I should even try to fight it ... maybe just add acid when I have people coming over to swim.

 

[easttn]

Have you tested for borates? It is possible to have borates and not know it which would explain why your adding more acid. Some trichlor and dichlor products have borates amongst other things in them and may not tell you about them. Take for instance the Dichlor shock product by Aqua Chem:
Aqua Chem Shock Plus

 

[JasonLion]

Since your fill water is high in TA, you are going to be much better off if you get an automatic acid feed system of some kind. In a dry hot climate you will be frequently topping off the water level, and TA will go up each time you do that. The only way to keep TA at constant levels will be frequent acid additions.