Not sure if [treiher] still "active", but I was searching for pretty much what he described because I've had these spots in my pool pretty much since around the first year of use. Now after being on this forum, I'm ready to tackle it.

I have a small number of these oval shaped brown spots no longer than a quarter size in diameter (and the narrow side is much narrower than that -- about the width of a pencil or a little larger). Most have occurred in the deep end of the pool on the sunnier side, but I see others in a few other places as well. This had me thinking algae at first, but I'm pretty sure it's a metal stain.

We have two stainless steel metal bars in the pool (under the water) along one side (the sunny side again) in the shallow end each having 3 attachments to the wall (under water). One of these bars has 2 of its attachments that have reddish-brown rust and a stain flowing down an inch or two from the attachment hole and this hole looks metallic, but not stainless steel. My hunch is that this rust occurred a year and a half ago when I was using TriChlor tablets in a floater since the floater was tethered somewhat near that area (though I would push it towards the center of the pool after closing the cover. So my guess is that the acidity from the Tri-Chlor caused the rusting.

However, even though I've been off Tri-Chlor for about a year and a half, it looks like there is still additional rusting occurring although very slowly. My numbers are as follows:

pH 7.4-7.5
TA 110
FC 3 (2-4)
CC 0
CYA 15-20 (hard to tell since < 30, but probably in this range)
CH 260
TDS 700 (estimate)
Volume: 16,000 Gallons (16'x32' but with interior ramp and side seat that take up volume)
Temp. 88ºF
Type: Plaster over gunnite (I think) with tile/grout around the surface edge.

I have an electric opaque pool cover so have little chlorine usage (about 0.5 ppm per day) and virtually no pH drift. I use liquid chlorine (12.5%) and occasionaly Muriatic Acid when needed (which is not often). I have also been on half-doses (i.e. every other week) of clarifier (I have a cartridge filter), enzyme scum removal, polyquat algaecide, and MPS shock, mostly because I get these free from a friend who works for a company that, among other things, makes pool specialty chemicals. I'm thinking of cutting back or eliminating these extras based on this forum (obviously not for economic reasons, but to simplify pool maintenance).

My questions are:
1) How can I remove the small stains on the floor of the pool?
2) Will this also work to remove the much more intense stain at the metal bar attachments?
3) How can I prevent or stop the rusting of the metal bars, assuming they are in fact still rusting?
4) How can I prevent future stains from occurring on the plaster?
5) In case I'm wrong about these being stains, how can I tell for certain that they are not some form of algae?

Thanks in advance for your help.

Richard