Cleaning stuff off bottom of pool

[Not sure if this belongs in this topic, this is as close as I could come to a "cleaning" topic :)]

All,

New ptec (about a month old). Recently I noticed a whiteish stain of some kind on the pool floor, in the deep end. Diving down with goggles, an up close inspection revealed that there is some kind of white residue clinging in between the pebbles, and it won't brush off with a brush. I'm thinking is some kind of scale, maybe from chemicals dumped into the water? Anyhow, I was thinking maybe a string acid wash would get rid of it (it's only about 1-2 sq ft. in size). But how to apply the acid underwater? I don't want to bathe the entire pool in acid just to remove a small stain. Any tricks for doing this? I am leery of diving down with acid, letting it go in the pool, and trying to scrub. The acid would surely surround me quickly :-/

Have you been dumping powdered chemicals straight in the pool without dissolving them in a bucket first? Have you got a good water test showing alkalinity, pH, Calcium and TDS?

I have dumped powdered chemicals into the pool in the past. I honestly cannot remember if the "stain" appeared before or after I did that, but I believe it was after. I dumped powdered shock, yellow-out, some calcium chloride, and some stabilizer into the water (broadcasted it) several weeks ago. This was before discovering poolsolutions.com. I no longer do that, but this may have been why I got the stain. Not sure. I'll try to take a picture of it later when the stain shows up better (it shows up better in the evening, when the sun is low).

My chemistry is somewhat balanced:

FC: 4 CC: 0
pH: 7.6
CYA: 50
Total Alk: 80 ppm
Calcium Hardness: 500 (thanks to the crappy drops-based kit I got, see http://www.poolforum.com/pf2/showthread.php?t=1112 for details).
TDS: ? (never tested this, I thought this was one of those "pool store" measurements designed to get you to buy chemicals but has no real effect on pools)

Maybe my CH has been high all along, allowing junk to precipitate out? The stain looks very much like someone took a handful of a dry power and dropped it, since the pattern on the pool looks like that. I just wonder if that was the case, why it can't be brushed off with brush. How does it cling, and not get dissolved?

Not a real safe thing to do but I have taken muratic acid, put it in a 2 oz container with a lid, swam down and opened it and set it on top of a stain. Acid is heavier then water so it tends to sink, it cleaned up the stain quite well. A larger stain could be a pain though.

It seems to me that one could take a piece of PVC pipe and hold one end on the stain with the other above water. Pour the acid in the pipe, and it would pretty well go directly to the stain. Much safer than being in there with it. It would be more complicated than this for safety purposes, and you'd better be sure you want acid on your pool.

You could even plumb a hose to the pipe with a valve so you could rinse afterwards