toxic water

Freshwater fish constantly dying! Hi all. New to posting on this forum but have been following threads for quite some time. I've been keeing fish for some 20 years. Parameters. Tank 75gal. Cycled for 2 months fishless cycle. Substrate: caribsea moon sand Filter: sunsun 304b (450gal/hr) Two...

My fresh water tank has raised my goldfish for years, they are massive and healthy. 3 boys and 1 girl. Lately, my water is starting to get a green tinge to it... is this caused from Algae or something else? The fish don't seem to be bothered, but I don't want it to turn into something that may...