Black Algae Killed by pucks

[CTIGuy]

Richard

Do you think the white crust, etched Spas tiles and black algae had anthing to do with adding too much CYA at one time? I added 8lbs one day and another 8lbs the next. I was going to add another but stopped when I noticed the white crust and black algae.

If so do you have any suggestions as to how to add large ammounts of CYA without getting the damage or black algae?

On Cl level the Install and Ops guide from the Mfg of the CL Generator http://www.jandy-downloads.com/pdfs/H05675-RevE.pdf on page 18 says "Free Chlorine 1.0 - 3.0 PPM. Above 3.0 PPM may cause corrosion of
pool metals." Is this just more bad information from the Mfg? On the same page above "The AquaPure is warranted to operate properly
only if these conditions are met." Seems like a catch22?

[chem geek]

It is the ratio of the Free Chlorine (FC) and Cyanuric Acid (CYA) levels that determines the rate of corrosion from the chlorine. The SWG industry's own studies showed that (here). The SWG manufacturers have always listed 1-3 ppm FC when that is clearly not correct. Most SWG users are able to run at 3 ppm FC with 60-80 ppm CYA, but not all. This does seem to keep away the free-floating green algae due to superchlorination in the cell (we think), but it does not good for algae stuck on pool surfaces.

I would not worry about corrosion of metal at the higher FC level so long as you have CYA in the pool. At least this particular vendor is disclosing the increased corrosion rates that can occur due to higher salt levels, but really the 3 ppm FC limit doesn't take into account CYA levels. Indoor pools without CYA will have a real corrosion problem even at 3 ppm FC as a couple of users found out with their stainless steel, but having CYA in the pool significantly reduces such corrosion rates.

So though I think your pool will be fine at Ben's chlorine/CYA table levels, I'm not sure what to suggest given their warranty requirements. It is a catch-22.

Richard