So this is all new to me but this CYA issue has been going on 20-30 years or more. Surely the Tri-clo manufacturers know this. So how do large commercial pools do it they don't use bleach do they? Some regulations for commercial pool are as low as 40 CYA so why the heck do puck manufacturers put in 50% CYA. A company like Clorox has nothing really to gain from overdosing peoples pools until they have issues really on local pool stores.
Is there any puck manufacturer that make low dose or no dose CYA?
The CYA is not added to the pucks. It's part of the chemical itself. The pucks are Trichloroisocyanuric acid (aka trichloro-s-triazine) and more commonly known as Trichlor. It's basically CYA with three chlorine attached to it (compare
Trichlor to
CYA). It is a single chemical so for ALL Trichlor no matter the manufacturer for every 10 ppm Free Chlorine (FC) they also increase Cyanuric Acid (CYA) by 6 ppm. It was a coincidence that you ran into problems when using the Clorox brand. They may not be compressing their pucks as much so by dissolving faster you used more chorine so added CYA more quickly than you usually do so you crossed over the edge to get algae growth because your FC/CYA ratio got too low (because your CYA level got too high so when you dropped the FC lower the ratio got low and algae could then grow faster than chlorine could kill it). It's also possible that the other pucks you used to use had an algaecide in them such as copper.
The active chlorine (hypochlorous acid) level that kills algae is proportional to the FC/CYA ratio. So at higher CYA levels you'd need to raise your FC proportionally to prevent algae growth. Alternatively, you can use chlorinating liquid or bleach that does not increase the CYA level; they only increase the FC level (and salt, but all chlorine sources increase salt since chlorine converts to chloride salt when it is used/consumed).
Commercial/public pools that have higher bather loads mostly use chlorinating liquid, some use saltwater chlorine generators, a small number use chlorine gas, and some use Cal-Hypo with sufficient water dilution to keep Calcium Hardness (CH) in check. Only commercial pools with lower bather loads use Trichlor and even then they have to drain/dilute the water when the CYA exceeds the state limit which is 100 ppm or lower. New York bans CYA (and therefore use of stabilized chlorine) in commercial/public pools completely.
Basically, Trichlor is primarily a residential pool product. It is convenient because the chlorine is concentrated so is less weight to carry and it is slow-dissolving. Instead of the pool industry being up-front about the problems of rising CYA with Trichlor, they instead get to sell you all kinds of supplemental products that are higher margin (profit) including algaecides, phosphate removers, clarifiers, flocculants, enzymes, etc. Some pools are naturally low in algae nutrient levels (e.g. phosphates and nitrates) so don't get algae in spite of higher CYA levels (lower FC/CYA ratios) and the existence of such pools has many people not believe in the FC/CYA ratio because they see it as refuting CYA having anything to do with algae growth. You, too, would probably have sworn that there is no such relationship because you never had a problem for 12 seasons. Now you know better.
