Water discoloration and crust

Question
We have a large tank which currently holds a large plecostomus and once held cichlids as well. Recently the tank has taken on a rather yellow hue (but the water is not cloudy). Also, a difficult-to-remove brownish crust has collected on the lid to the tank (and only on the lid).

We have no driftwood in the tank, our decorations have not given us trouble in the past, the plants and glass are clean and clear, the gravel is mostly clean and we added large amounts of fresh water to the tank to try and clear the problem. So far, nothing has helped. Any ideas of what this is or how to fix it? Thank you in advance!

Answer
Hello Mary,

The first thing I would ask is if you use tap or well water because these both have alot of minerals that can turn the water this color. Tap water or well water wont necessarly hurt your fish however you need to test the water you use to make sure it has the right properties (pH,ect.) if you could please send me a follow up telling me what kind of water you use and if you test it i can give you further assistance.

Thanks,
Exp. Michael M.

Sorry for the time it took as I have been really busy but follow ups always go alot faster. Normally the same day you send it in.