Pool Stains...help

I posted a few things last year and this forum really helped me out, I really appreciate all the help last year. I have ran into another problem at the Apartment Complex Pool that I take care of. Within the past 6 months or so, i have noticed these hockey size/shape brownish stains at the bottom of the pool. I have tried taking a pumice stone and rubbing on it lightly and doesn't work. I have tried taking some PVC pipe and pouring down some Muriatic Acid on the stains and did not work. So the last thing I tried and it worked, was taking a 3 inch stabilized chlorine tablet and letting it sit on the stain for about 10mins. BAM! it worked the stain was gone. I did have the metals tested a few months ago and they said the copper levels were kind of high, I do not remember the exact number. So since then i have been adding a bottle of Metal out once every 2 weeks. I can get the water retested for copper. So I guess it's copper in the water that is causing these stains?

My question is why do the chlorine tablets work and not the pumice stone or Muriatic Acid? I would think the Acid would work easily, it burns off the first layer of plaster off right?

Chemical Levels
CH 300
pH 7.3
TA 105
CYA 55
FC 5
TC 4

I think the pool is around 35k gallons or a bit larger.

Thanks!

Can't tell you why TC tabs would work. If it was iron, acid would probably work.

I can tell you that most (maybe, all?) of the hockey puck stains I've ever seen were caused by TC tabs being tossed on the pool bottom. Could that be the case here?

Ben

Naw no TC tabs were tossed to the bottom of the pool. I will try and take some pictures of the stains to show you. The stains just started up slowly, like i noticed 1 then started multiplying. Now there is at least 30ish all around the bottom of the pool.