WetScapes

Heldor went belly up, SCP bought what ever was remaining. Their filters were made by Hayward. You could probably putt in about 200#- 250# of sand, Zeobright tends to dissolve, or better yet upgrade to an element cartridge filter ( a lot less maint.)

The LM3-40 from Zodiak will handle up to 40.000 gal. As far as steps go, I always glue down wall foam on the treads, under the liner, to help give some traction. Some copmanys offer a textured liner for steps.

I have switched to element/cartridge filters on all my pools. Less maintenance and more efficient than sand. And no back washing, so no loss of salt, since all my pools are saline. Just think... low maintanance.

sounds like a stabilizer block, too much cyanuric acid. The only way to fix is to dump 1/2 the water and refill.

CONVERT TO SALT

Mustard algae will not filter out, it just recirculates. You will need to treat with "yellow treat" or similar, and then vacuum on waste. You should really consider converting to a salt water chlorine generator, it makes maintenance a breeze.

I personally dislike Goldline Controlls (Aquarite) Out of the 15-20 that I've installed I've had call backs on probably 50%. Don't have any experience with the Ecomatic. What I install is the Zodiak LM2 series, I 've installed 100 - 120 of them and had probably 5-6 callbacks, a much better percentage. They are the easiest to install and work like a dream, very user friendly. Just my .02

If left to drain how low will the level actually go before it stops? If the pic shows this level, I'd suspect a failed glue joint in the spa plumbing, especially if flex pipe was used, have there been any pressure tests done to try and pin point the leak? Or has the light been checked for a broken conduit (that is the first place I usually check anyway) I know it's rare, but a bad seam in a liner will usually leak from the start. Sorry to hear about all your woes, I know a bad pool is a lot to deal with.