White flakes in pool

I have a 30,000 gal in ground pool with a SWG. It is about 8 years old. My robotic cleaner is constantly getting gummed up with white stuff. It is about the consistancy of wet, white sand. If I leave the robot out to dry instead of rinsing it off right away, the wet "sand" dries into white flakes. Today the pool bottom had visible mounds of white flakes which I'd never seen before. The pH was about 7.8. I figure the stuff is calcium that precipitated because of the high pH.

temp 82
Ca 400
TA 90
cya 60
FC 2.5
CC 0
pH try to keep it about 7.3 to keep the saturation index close to zero but I am constantly having to add acid.


Here are my questions:

Would lowering the Ca help? If so, how do I do this?

I don't like that I am constantly (at least once a week) finding my pool with a high pH (>7.6) and then having to add acid. I thought buffers were supposed to help hold the pH more constant. Maybe without buffers I'd have to add acid every day. But the reason I ask this is that I saw one post regarding a similar problem with flakes in a SWG pool suggest adding borax as a "second buffer". But in reading the sticky posts in this forum I saw that borax only raises pH which is definately not what I need. And I thought that TA is a measure of buffering capacity and I'm already on the high end of normal for that. So what is it, do I add borax to make my pool more resistant to pH changes or not? Do I just keep adding acid and try to keep my saturation index close to 0? And do I just have to live with the fact that despite my best efforts I am constantly having Ca precipitate in my pool gumming up the robot?

Thanks,

Steve

Hi Steve, I'm sorry I can't answer your questions, but someone who can will be along shortly. In the meantime, you should post the particulars of your pool and equipment, is it vinyl, fiberglass, or gunite, the type of pump and also the type of filter. This will help the mods to give you the appropriate advice. Good luck.

Tom

I can't say what the flakes are, but with respect to borates. They can act as a buffer to pH change. I added them to my pool (I also have a swcg) and went from having to add acid weekly to having to add every two or three weeks. It does increase pH, so you have to add carefully and dose with lots of acid to keep pH from getting too high. Instructions for how to do it are here: http://www.poolforum.com/pf2/showthread.php?18597 . One thing to remember is that "making it resistant to pH change" goes both ways. You add acid less frequently, yes - but you end up putting larger doses in when it comes time to drop the pH back down. You spend about the same amount of money on acid, it's just less work to add acid less frequently.

Where do you have your SWCG output level set to (usually there is a knob to control the output level via limiting "on" time)? Also, check your swcg manual for a recommended CYA concentration. Mine wants the cya to be at 90ppm, and salt at 3200ppm (I didn't see a salt reading in your post). Make sure these are both at the recommended level for your SWCG, and hopefully you will be able to turn down the swcg's output - which will in turn increases the lifespan of the cell as well as reducing how quickly the pH rises.

Another cause of pH rise would be aeration from water features/returns etc. Do you have water features that aerate the water? Are your return eyes pointed up so they rifle the top of the water? If so, you may want to consider running the water feature less or pointing the return eyes a little more "down".

If that white stuff ends up being calcium (and I'm not saying it is, someone else will have to chime in there) then you probably also need to clean and maybe acid wash your cell. One thought I had; several times I have had pool toys and other stuff (clothing, etc) in the pool that was getting broken down. One time I fought with this pink semi slimy gross substance appearing in my pool that would not die when shocked. I spent hours scooping it out every day, and it turned out to be one of those "noodles" that my kids play with was getting old and breaking down. The material from the inside of it was actually separating from the noodle and floating around.

Thanks. It's a gunnite pool and I didn't mention my salt level because my generator reads 3200 (just shy of the recommended 3500). But I've been suspicious because I've added a lot of water (to replace evaporative losses and splashing/carry out) and haven't added salt for a couple years. Just got some test strips and they read 2500.

But now I am confused and need the help of a chemist. You said that turning down the output of my SWG would "reduce how quickly the pH rises." Are you saying that the SWG somehow makes the water more basic? You don't happen to have a chemical equation to feed my curiosity do you? I suppose it doesn't really matter but I've always wondered why I need to constantly add acid.

Steve

There are folks on this forum that are chemists and that can feed your curiosity, and I'm not one of them, but basically, yes--the operation of the SWCG releases carbon dioxide that is gassed off, which leaves the water more basic than it was. Rising pH is a normal part of SWCG operation, but adding borates as Kelemvor suggested, and keeping the TA on the low side, can help reduce the rate of the pH rise.