I believe it is deposits from using Lanthanum chloride in the tank. I tried vinegar to clean a skimmer cup with lanthanum deposits. No success.
I dont think it is possible to remove that with vinegar. Maybe with a weak sodumhydroxide solution but i dont know the risk of that etching the glass.
I dont think it is possible to remove that with vinegar. Maybe with a weak sodumhydroxide solution but i dont know the risk of that etching the glass.