Tan/Brown Staining Question

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G

Gaidal

0
May 23, 2011
11
Hey guys,

Really enjoy this forum.

I, like many with "pool questions" inherited a beautiful 20k in-ground plaster finished pool with my new house in central Virginia. The pool underwent an overhaul about 1.5 years ago with a new plaster finish and brickwork/tiling around the edge of the pool.

I opened the pool this year with a high pH (~8.0 per ColorQ) and low CH (~120). I threw some calcium chloride in to raise the CH to about 180. Other test results: TA ~60, CYA 40. Water was pea green so i shocked with liquid bleach and did a whole lot of vacuuming per instructions on this board. Pool cleared up nicely and I am adding about a 96oz jug of bleach every other day while waiting on a SWG to be installed.

I have several areas of widespread discoloration... some patches on the sides of the pool, but primarily on the bottom. In particular around where my two returns enter the pool (I have none on the side and three returns plus a main drain on the bottom). The entire bottom surface of the pool has a relatively rough feel.... not terrible, but kind of like a fine grit sandpaper - not really actually bothersome other than the discoloration since it gives a little bit of traction. It doesn't seem to be better or worse where the discoloration is. Ironically the surface around the water line is very smooth but further down gets somewhat rough.

Current test results are:
TC - 3-5
pH 7.2-7.4 (presuming this is calcium scale, I've lowered the pH to this level)
TA ~80 (assuming it increased due to liquid bleach)
CYA ~40
CH ~120-140 (this is with the Color Q... I actually can NOT get the test to register with the Taylor drop test...).

So I had been operating with the assumption that this is scale, but I read today that etching can also cause tan brown stains. So I'm a little freaked out by that since the plaster job was new and I guess this is possible with the low CH... will post some pictures later. The stains definitely look more pronounced in the shade.

My main question is: etching vs. scaling. My second question would be what is the proper CH balance if you ARE fighting scale? I don't want it to drop too low, do I?

Edit: I should add that I do not know what the readings prior to closing since we moved in after the cover was on. The pool guy who did the plaster job did warn me about high pH over the winter but having absolutely no clue about what I was doing I added some muriatic acid blindly about halfway through winter and just swept it around as much as I could with a pool handle vacuum.
 
Do the stains look like this?
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That's calcium scale. It can be slooooowly removed by keeping CSI negative and brushing with a stainless steel brush. Steel pool brush, not something harsh to strip paint. I keep meaning to take some progress pictures, that particular patch is almost gone from my spa. By slooooow, I mean roughly a year.
 
Sort of but more tan. There is definitely some patterning to it. Hopefully the pictures later will be more helpful.

I did get a stainless steel pool brush which so far has not done a whole lot to it. I do see some cloudiness when I brush it but that could just be dirt on the bottom too. :)

Still freaked out about etching....
 
I still think it looks like calcium scaling.

But it could be metal staining, which is easy enough to check. Ask your wife for a few Vitamin C tablets. Or go buy some at Walgreens, CVS, Riteaid, wherever. Store brand is fine. Lay the tablets on the stain. It may take an hour or so until they "melt." When you just can't wait any longer, clear the residue off and see if you have clear patches. If you do, you can search for "AA treatment" or "Metal stains" or just post again.

If it doesn't change, then see if you can scrounge up a chlorine tablet. One of the neighbors probably uses them in their floater. Sometimes the pool stores have them individually wrapped on the counter, as well. Lay it on a stain and see if it bleaches out any. If yes, organic stains, and a summer with FC at the upper end of the range should bleach it out.
 
Yeah I did read about the vitamin C test which I will give a shot.

If it does end up being calcium scale, where should I keep my CSI for a "chronic" treatment? Currently I'm slightly under -0.6 which is getting into corrosive water. Would it be better to have a lower pH and a moderate level of CH or a pH like I have now with a low CH? Or does it matter at all?
 
I've been keeping my CSI between -.4 and -.6 with CH over 500 (hard fill water), and like I originally posted, it's extremely slow. It's going to be nearly impossible to maintain the CSI down there over the summer, because I want to keep pH 7.4-7.5 when we're actually going to be swimming in it. I expect by this time next year, my pool surface will be pristine.
 
OK good to know. Since I'm switching to a SWG pretty soon I probably will go ahead and start getting my CH back up since the salt seems to add quite a bit to the CSI.

I'll report back with the results of the AA test. Do not have access to a chlorine puck but I'll see what I can find. It definitely COULD be organic staining since the leaves were collected most prominently in the two areas with the most staining so we'll see.

CaCl is freaking expensive, btw... at least when you need to add 30 lbs of it! Need to wait until winter to get the de-icer stuff stockpiled.
 
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