White powder on walls

[Terrys379]

What do I do to remove and keep white residue off painted fiberglass. Brush won’t take it off but it comes off when you run a finger through it.
FC: 7
PH: 7.6
AK: 70
CH 210
CYA 50

F

 

[Texas Splash]

You say painted, but this is basically the original gelcoat correct? If so, this is a somewhat unusual issue and different from the more common issue of FG pools that get a consistent, almost solid-white chalky finish all over below the waterline that does not rub off by hand. I've seen your scenario on some other threads buried deep in the forum, but I can't seem to find the exact post(s). Let's be clear first, your test numbers above look perfect, so there is no reasonable explanation why that is happening. If you have not added any unusual pool store products to the water, it may be something unique to your gelcoat application. If this is a new pool, you should call the manufacture first to discuss the issue wit them

Now I say the following with a bit of caution and TFP disclaimer because your numbers already look great. But in fairness to the other FG pools who had white stuff that wiped away by hand, I seem to recall that those other FG pools saw improvement by increasing the CH and/or TA a bit. It doesn't make sense and I don't know why because in theory, today's FG pools do not have calcium in them so they should not require CH, but for some reason it helped them. The problem with changing your chemistry is that it can effect other things like pH or CSI. CSI shouldn't matter to our FG pools either (no calcium) but some FG pools are having odd reactions to what appears to be good water chemistry.

So here are some options I think you have at your disposal:
1. Contact your manufacture if you can to open a discussion on the issue. Standard manufacture reply - "Do you have pool store test results?" They will do anything they can to avoid a warranty claim.
2. If you decide to try and adjust the TA or CH, do the TA first since it's the easier of the two to lower later. Remember that increasing the TA (say 100-120) can immediately cause the pH to want to climb a bit. It could cause a cycle of up & downs with acid which we normally try to avoid, but it would be interesting to see if elevating the TA helps at all. If not, then lowering it again with acid is not the worst thing.
3. If the TA change shows no improvement, there's always the CH. Again, not typically known to be required in our FG pools, but for "some" FG pools out there, increasing the CH to about 300-350 seemed to help with this odd situation of white stuff wiping off by hand. If later the CH doesn't seem to help, I'm sure you can always lower it over the season with water exchange from seasonal rains.

For some FG pools, the reactions we're seeing do not make sense. But you can try the items above if you like and let us know if there is any improvement. Best of luck and let us know.

 

[Terrys379]

It’s been painted over original Gelcoat twice with the most recent in April. I found the same thing reading in the forum about raising TA and CH. I just raised TA last night from 70 to 90 so we’ll see what happens.

 

[Texas Splash]

It’s been painted over original Gelcoat twice with the most recent in April.

I see. Well, that probably changes the dynamics of it all, but at this point I suppose anything is worth a try. Good luck!