Low Ph And Staining Problems. Help!

[Pete Rittwage]

(cross-posted from Aboveground Pools)

I am a relative beginner to pool chemistry. I bought a house 2 years ago with a 21' round old above ground pool with a new liner. I am able to shock and use algecide to get rid of algae and get the water clear, but this year when I opened the pool (Georgia, Southeast USA) my kids said the water "tasted funny". Not that they should be tasting it, but...

Anyway, I tested the water and Ph was low off the scale. The test shows light yellow (below 6.8). I bought a 10 pound bag of Arm and Hammer and added a pound at a time over the weekend until it was gone, but it only turned a little darker yellow on the test. The TA test shows about 50.

However, even with the still low Ph, when I added the baking soda, the bottom and sides of the pool stained badly. Ugly yellow steps (were white as snow) and an ugly yellow ring and ugly yellow stains all over the bottom. This stain will go away when rubbing Vitamin C on it, but it comes back the next day. It is not orange or brown.

Should I be getting this staining even with the Ph that low? I lowered it back down to see by putting in a pound of Ph reducer, and the stains went away again, but this can't be good.

I also let the Chlorine go to 0 and put in two quarts of Metal Out and ran for a couple days, then raised the Ph back up, still ugly stains came back.

What am I doing wrong?

[chem geek]

It sounds like your pH and TA "crashed", possibly from continued use of Trichlor pucks/tabs (which are acidic) without checking the pH and using pH Up and/or baking soda periodically. The low pH possibly corroded metal in your pool -- possibly copper in a heat exchanger in a gas heater and possibly iron from steel or stainless steel in the pool. You should have your water tested for metals. Since you are seeing staining even at low pH, you may have an extraordinarily high level of metals in the pool such that a metal sequestrant would be impractical and water replacement might be needed. When you raised the pH back up, at what pH did the stains start to reappear?

You are basically doing the right things. You can read Metals in the Water and Metal Stains for more info. Just note that baking soda mostly raises TA. It should not be used to adjust pH, at least not by itself. If both pH and TA are low, then pH Up (or Arm & Hammer Super Washing Soda which is the same thing, sodium carbonate) is a better choice for getting the pH up quickly (along with TA). If the TA is already high enough and you just want to raise the pH, you can use 20 Mule Team Borax which raises the TA half as much as pH Up, or you can aerate the water which raises the pH with no change in TA (though this only works well if the TA is not low).

You should also read other parts of the Pool School to avoid this problem in the future by more carefully managing your water chemistry. This includes getting a good test kit, either the Taylor K-2006 or the TF100 from tftestkits.net.

[Pete Rittwage]

Thanks very much for the reply. I get the staining before I even get to 6.8 on the pH scale, unfortunately. I am sure you are correct, though. Sometime over the winter, the pH crashed for some reason. It was OK last season.

Is there a manual metal test or should I take some water to a pool store? I am afraid if I try to drain the pool I may have to get a new liner, since it's kind of wrinkled and folded in places now...

[chem geek]

The metal tests (for individuals) are very expensive (a combination test for copper and iron is the Taylor K-1264) so you'll need to go to the pool store -- most have the metal tests and will test for free.

[Pete Rittwage]

They said it was iron, but not bad enough to drain and refill. No idea where it came from- there is no exposed metal that I can find in the filter or pump (it's all plastic), no heater (I'm in Georgia!) and the skimmer has no exposed edges. There is a stain on the bottom where a key was left, but it is old (before I had the pool 3 years ago).

I ended up putting in a quart of "Jack's The Pink Stuff" and following the directions. After that, I added about 30 lbs (really) of Baking Soda to get it back balanced and so far, it's crystal clear and all tests are perfect.

Now, there is no Chlorine at all in it, so hopefully it won't come back as soon as I add that.

No more of those floaters with tabs for me. I talked to several people at the pool store and they said they constantly had problems using them...