Water Balance for AG Heater

[ssabin]

I have a new AG 27' round pool that is about 6 weeks old now. The water is very clear, but my water balance is a little corrosive:

FC: 4.0
CC: 0.0
pH: 7.3
TA: 130
CH: 100
CYA: 35
temp: 85 deg F

I've been keeping the FC above 3.0, and the water has been sparkling clear. We have a solar cover that we keep on almost all the time and have not yet used the gas heater. In fact, the gas line to the heater is still not complete (although the 140-foot trench is complete). The 2-speed 1.5 HP pump has only run on low speed since the electrical service is just now near completion - it's running on a long extension cord now which has too much voltage drop for the high speed to run. So I've never vacuumed and other than some sand, the pool still looks great.

For my initial pool fill, I had city water trucked in, which put most of these numbers where they are without adjustment. I just added my first top-off from my softened well water, and I have TA about 280 and CH=0 in that softened water. Unsoftened has iron in it, and is not an option at this time (I may create a filter adaptor that I can attach to my hose to remove the rust, but that's a low priority for now).

The water flow goes from my filter through the heater and back into the pool. Since my water balance is slightly corrosive, I am considering taking the heater out of the water loop for the hotter months, or until I get the water balanced. Or should I add some CH and raise my pH and keep the heater in the loop? I just started an attempt to aerate with the return eyeball pointed up and keeping the cover off during the day, and the pH raised from 7.2 to 7.3 in one day. Is there any other reason to be worried about water balance besides the heater (like the pump)? I kind of like having the pH on the lower side, and it appears that the solar cover usage is keeping the need for bleach low and the temps high.

Oh, the heater is a Rheem 206, which has the plastic headers and copper tubes between them.

Thanks!

 

[duraleigh]

Hi, Scott, Welcome to the forum!

I may learn something here but see I nothing to indicate your water is corrosive. Your pH is is virtually perfect and your T/A could be lowered a bit but you're certainly not in a danger area.

Your low Ch suggests scaling should not be a problem unless, somehow, you let the pH or Alk COMPLETELY run away......something that you obviously won't do since you've done such careful work to this point.

I would say that getting the Alk down to maybe 100 or so thru aeration and muriatic would be the final touch in having perfect pool water.....but, that said, you're pretty darn close, anyway.

If I'm missing something as to why you feel the water is corrosive, post back....it will certainly not be the first or last time I will be incorrect :lol:

 

[JasonLion]

Welcome to TFP!

What you are calling corrosive water I would call a low calcium saturation index. The general wisdom these days is that calcium saturation doesn't make any difference in a vinyl lined pool as long as it doesn't get too high and start scaling or if you have something whose warranty requires particular numbers. So you can leave things the way they are and shouldn't have problems.

You might want to lower your TA a little. If you keep your PH low and are refilling with TA 280 water the PH is likely to be drifting up fairly reguarly. You can either add acid reguarly or bring the TA down now. Either approach will use the same amount of acid, it's more a question of when you want to do the work.

As long as you keep the PH above 7.0 you shouldn't have any issues with the pump, heater, or liner. PH below 7.0 can damage both the heater and the liner. Pumps seem to be pretty resiliant. A slightly higher PH, say 7.5, would be a little easier on your eyes and slow any PH rise from high TA.

 

[ssabin]

Thanks for the quick replies. The reason I think the water is a bit on the corrosive side is from the Langelier Index, where I believe I'm around -0.5 or -0.6. Specifically, I have Chem Geek's spreadsheet, although his comments indicate that -0.2 is an optimal target when using a heater.

The heater literature mentions some pointers for good water balance, but I belive that to be a general guideline more than a requirement for warranty. It does, however, state that FC should never be allowed to go higher than 5.0 ppm!

Perhaps I'm just micro-adjusting here?

 

[JasonLion]

Over the last year or two there has been some debate on the imporatance of a negative Langelier Index for vinyl lined pools. The majority opinion right now seems to be that even noticeably negative numbers are fine as long as you don't have any plaster/tile/grout/stone/pebbles in constant contact with the water.

Never allowing FC to go above 5 ppm seems to be left over from the times when people didn't understand the chlorine CYA relationship. If you don't have any CYA in the water a FC above 5 can be a real problem. But with 30 ppm of CYA you would need to raise FC above 28 to have the same corrosion risks.