very high alkalinity and ph is not stable

[cantera]

I have an above ground metal frame pool. I purchased it from walmart. It is 24 ft. round and holds 12000 gallons. I opted for the salt water pump instead of having to mess with the cholorine. My alkalinity is very high, about 600. my ph can be from 7.4 to 8.2 according to the kit I am using. I am using the hth 6 way test kit that i purchased from walmart also, probably not the best. I have already called the hth hotline and they told me to put ph minus in it to lower the alkalinity first then work on the ph. well my alkalinity is not lowering at all but my ph has. The problem is i continuously have to put the ph minus in everyday or every other day just to keep it at a good level so the kids can get in. it is getting pretty expensive. My total cholorine is 3 and bromine is 6. The water is very clear. There is some cloudiness after about 6 hours of the kids being in but it is still clear and you can see the bottom with no problem. The water is crystal clear again after the salt water pump has run for 12 hours. The total hardness level is 0. We have very soft water. The cyanuric level is 50. Please help. We are going to go broke buying ph minus. I have to special needs girls who want to be in it all the time. They have a lot of fun and don't even realize we are using this as water therapy for them too.

[chem geek]

First of all, get yourself a proper test kit, the Taylor K-2006 kit you can get at a good online price here or the TF100 kit from tftestkits(dot)com here with the latter kit having 36% more volume of reagents so comparably priced "per test".

How did your Total Alkalinity (TA) level get so high? Test your fill water to see it's TA level. If it's much lower, then a partial drain/refill will be the faster and easier way to lower the TA. Otherwise, it's going to take a LOT of acid to lower the TA and the fastest way, but still a pain, is to follow the procedure outlined in this post. If your TA is truly 600 ppm, then to lower it to 100 ppm will take a cumulative 12 gallons of acid -- obviously not added all at once. The TA lowering procedure simply speeds up the process that you are going through now. Again, if your fill water is significantly lower in TA, then a partial drain/refill will probably be easier at least to start with and then you can use the procedure to lower the TA the rest of the way.

As a separate issue, you should have at least some Calcium Hardness (CH) in the water though you don't need very much since you have a vinyl pool. I'd still have at least 50 ppm, but that has nothing to do with your high TA problem.

[cantera]

Do i have to dilute the acid in a bucket of water first or do i just pour it in the water? It is okay that I do it a little at a time, like maybe 20 oz. at a time to lower the ph? I don't want the ph to get too low. If it doesn't get it low enough than i will just put a little more right? Of course not 20 oz.
by the way my ph is about 8.4 Thank you for all of your help.

[chem geek]

You do not need to dilute the acid, but you do need to pour it very slowly over a return flow with the pump running (in the deep end, if you have one) and then after you've added it lightly brush the side and bottom of the pool in the area where it's been added. And yes, you can always add less acid, remeasure the pH (after about a half hour if your circulation is good) and then add more as needed.

[Guest]

I have already put 30 oz. of the acid. The ph is at 8. Am i not putting enough in at a time or should i continue to add a little at a time? So sorry. This is our first pool.

[chem geek]

With a high TA of 600 ppm, if it truly is that high, the pH will not move very much even with 30 ounces of acid. In theory it would drop from 8.4 to 8.23 so since you saw it move to 8.0 I suspect that the TA is really lower, perhaps around 300 or even lower. You can continue to add more acid -- even 64 ounces (8 cups) would only bring down your pH to around 7.4 if your TA were 300 ppm. As the pH gets lower, it will tend to bounce back up over time due to the high TA. Essentially, pools are over-carbonated, but your pool is way too carbonated so it outgasses carbon dioxide faster than most and that causes the pH to rise.