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I was wondering if I should stop using muriatic acid and see if my PH will stabilize at 7.6. Would this be a bad idea? Mine has been reading around 7.6/7.7, and daily I'm adding about .75 pints to push down to 7.5...is this a waste of time/chemicals?
I guess what I'm asking is, if my pool will stabilize on it's own somewhere between 7.2-7.8, should I just leave it alone?
steveinaz,
Since your signature line says you have a saltwater chlorinator, I suspect that the rise in pH you are seeing is due to the outgassing of carbon dioxide. Can you post some of your pool water chemistry numbers? In particular, if your TA is higher than 80 (assuming a CYA of 70-80 as recommended by most SWG manufacturers; if your CYA is lower, say 30, then the TA can be 70), then your pH will have a stronger tendency to rise. Also, do you have aeration features such as a waterfall?
It is true that the rise in pH will slow down at higher pH so you can just settle on a higher pH, but lowering your TA will probably be the most effective way at slowing the pH rise down and significantly dropping the amount of acid you have to add. This thread talks more about this (but it's a long thread).
Another option, done in combination with lowering the TA, is to use 50 ppm Borates in your pool (from Borax and acid addition). This thread talks more about this, but is also a long thread.
I also noticed that in this thread that you note that your pool is new and is plaster/gunite. In that case, new plaster will "cure" and release calcium hydroxide causing your calcium hardness level to increase and the pH to dramatically increase. You will have to add lots of acid to compensate for this. The above suggestions for lowering the rate of increase of pH and acid usage are still valid (as they reduce the amount of carbon dioxide outgassing which is one source of rising pH), but even doing the above you will still have a significant demand for acid until your plaster cures. This is greatest in the first month, continues high for a few months, is much lower (sometimes not noticeable) after 6 months, and may not be noticeable anymore after 1 year (though some people report noticeable acid demand for up to 2 years). If after lowering the TA and settling for a higher pH (say, 7.7) you still find you need to add lots of acid, then the curing of plaster is most likely what is going on. There isn't anything you can do about that except realize it will eventually slow down.
Richard
Sure. Right now I'm using Clorox--SWCG isn't running yet (25 more days) FWIW, the pool is 7 days old:
FC=5ppm (lose about 1-1.2ppm per day)
CC=0ppm
PH=7.6
CYA=40
TA=200
CH=200
Currently, I'm adding about 2 pints of Clorox per day, and about .75 pints of muriatic acid to keep everything dead-on. I'm wondering if I'm being a little too anal on the PH by trying to get a perfect 7.5 everday. My fill water had a TA of 180 right from the tap, so I figured TA would be a little bit of a battle...
I've read thru both of those threads, extensively. The Borate discussion is especially interesting...
Well, you can see that your TA is exceptionally high (as you said, you had no choice since it was 180 out of the tap). If you follow Ben's Lowering Your Alkalinity procedure to lower your TA to at least down to 100 (if not 80), then that should help significantly. However, as I said above, your new plaster will still create a significant acid demand, but at least with the lower TA you won't be adding to the problem with carbon dioxide outgassing.
Happy aerating! If you have an air compressor with a nozzle that can produce small bubbles, that is particularly effective. Your SWG, when it comes on line, will also produce lots of tiny hydrogen bubbles. For my own pool, I used an outdoor portable shower with the head removed (or just having a hose directed at the pool from up high would work) and had it splash into the pool. If the rocks in your new picture photo are a waterfall (it's hard to tell -- it looks like they might be there as a visual feature rather than a waterfall), then turn that on as that is a good source of aeration.
Since your plaster if brand new, I'm not sure you want to lower the pH that much to 7.0 (as with the lowering your alkalinity procedure), but aeration certainly won't hurt and will speed up the lowering of the TA.
Richard
Ok, will do. I guess I'm trying to do too much, too fast. The plaster is only 7 days old. I'll run my waterfall, it creates quite abit of turbulence when on full. Thanks Richard, I appreciate you patience and help.
Well stock up on acid because you'll need a lot! You don't really have to do anything in a rush. With the high TA it's sort of a "pay me now or pay me later" situation. You'll end up adding the same amount of total acid over time to get the TA lower, but doing the aeration will speed that process up so you "get it over with" sooner (i.e. adding a lot of acid in a short period of time instead of less acid per day over a longer period of time). Hopefully when you are done, the rise in pH will be less, but it's really up to you. If you don't mind adding some acid every day that's fine; you'll just be doing that for quite a while, but eventually your TA will drop albeit slowly.
I calculate that for your 12,000 gallon pool with the numbers that you posted that it would take 38 cups of Muriatic Acid (31.45%) to reduce your TA from 200 to 100, along with aerating (outgassing) a little over half of the total carbonate in your pool. So, you'll be adding 38 cups of Muriatic Acid no matter what -- it's your choice of the timeframe over which that is done. This calculation does not take into account the additional Muriatic Acid needed to compensate for the curing of plaster -- that is not an easily predicted number. By the way, the 38 cups of acid plus the outgassing raises the chloride (measured as ppm sodium chloride) by 22 ppm, but the TDS actually gets reduced by 58 ppm due to the removal of (mostly) bicarbonate from the water that exceeds (in ppm) the addition of chloride from the acid.
Richard
I'll start the process tonight, acid/aeriate...etc. I'm gonna target TA @ 120ppm since I'll probably have an on-going battle with fill water @ 180ppm. Thanks Richard
Process: http://www.poolforum.com/pf2/showthread.php?t=6588