Hi All- first timer here Had a strange happening in my fish tank. I have a 20L with one black moor (I know, I got my fish before I knew better), I perform an ammonia test and water change every Tuesday and Saturday (30 - 50%, depending on levels). This morning I did my change, his ammonia was heading for .75. I did a 30% water change with a gravel siphon as it was very silty. I also cleaned the casing of the filter under tap water because the silt had blocked the grill, but cleaned the sponge in tank water. Ammonia is down to about .25 or so. Now after the change, the water is kind of yellow, like watered down Mountain Dew. It happened instantly. I've had greyish cloud after a water change before from silt, but never yellow. I put ager, aquarium salt and a half dose of ammonia neutralizer in the water as recommended by a guy at the fish shop- none of which are yellow tinged. The plastic plants and decorations have been recently replaced but were cleaned in tank water before I put them in, this is the third change after I put those in. The tank has been relatively recently cleaned from scratch, was fast-cycled chemically and I left the filter mucky for the first few days to try and recolonize the bacteria. The water was perfectly clear (give or take) before the change. My fish keeping ignorance (coupled with a power surge leading to a week with no filter) led me to an unfortunate ammonia related fish massacre, leaving 2 fish dead and the black moor the sole survivor (who, in true zombie-fish fashion, was pretty much dead at that point but was resurrected with an empty flour container and an oxy block). The only thing I can think of is that a little bit of the ammonia or ph testing fluid leaked into the water change bucket or something, there was a little bit of food-dye like substance in the sink after I packed up the fish cleaning stuff, but no evidence of it in the bucket. All the resources I could find online said that yellow meant it hadn't been cleaned, nothing resulting immediately from a clean. ETA: I should add there's no driftwood or anything like that in the tank, and the gravel is natural colors with some blue pebbles mixed in so it can't be coloring from those. There's also no light cause it blew with the power surge as well, and I haven't had the money to get a new one.