Be careful about that @Joshii. The alagecides with blue/copper add just that to your pool - copper. That's never good. Poly 60 is a TFP-recommended product, but typically only at winterization or during an AA treatment. Using algaecides with a normal FC level will not last as the chlorine will break it down and oxidize it faster.
@Enzoenzone, hang in there with the TFP discipline. Unless there is algae hidden and undisturbed, the proper amount of chlorine will kill it. Your light(s), are they the smaller LED nicheless kind, or is there an actual niche behind that might need to be inspected?
Also, I didn't ask early .... do you have a main drain? If so, covers can hold junk so they need to be exposed.
Lastly, don't underestimate the deep cleaning of the sand. If it's been a while, it can help.
Like I feared. I have the same issue with the cya. None in the water. I followed you method and before the SLAM it was at 50 taken over a few days. Now is depleted and it happened with the others SLAMS as well. The CH went down as well at 175. FC at 18. The PH is the only one who remains the same 7.2.
I attached a picture with the light. Do I need to lower the water level to take it out?
I am leaving in vacation on Monday and I tried to fix it before I go but this is it.