Suddenly Yellow Water

My husband's freshwater tank did the weirdest thing tonight. It suddenly got a strong yellow tint.

We unfortunately had a heater go on the fritz two days ago... the water hit 100 degrees overnight and killed the 7 tiger barbs... amazingly two plecos and two rainbow sharks survived. (The tank is 65 gallons) Waited for the water to cool, did a 25% water change, new heater, and cartridge change... everything seemed fine yesterday. Then today it did the color change, almost instantaneously.....

From what I've read here I saw it could be something in the tank, although all he has is gravel and some rocks that have all been there since the tank was set-up two months ago. (The heater was used from a friend) I checked the parameters and the nitrates were high... added 4 doses of Prime and one dose of turbostart to hopefully bring it down. this seems to be clearing up the color... but we're still curious what caused it and if there is anything else we need to do.

Any ideas?!

More mysteries....

The filter is a proaquatices that hangs on the back. Sorry I am at work and can't give more info. He just replaced with the same type of cartridge that he has used in the past. (it's a white floss "bag" with two narrow bags of carbon in them) (And I just checked he rinsed it in clear water)

To further the mystery... the water quickly cleared last night... looked fine when I left at 10 this morning... now at 12:15 my husband calls me to say his tank has turned red?! I've seen tanks do some crazy things, but this definitely takes it all......

He does have red gravel in the bottom... could the extreme heat have done something to that?

Mystery Solved

Just talked to our LFS. Seems our pH got soo low during this drama that the backteria aren't effective in cycling anything. Which has caused the color change. I have never seen anything change so dramatically in a fish tank. It has gone through the rainbow... red... yellow... orange... last night it looked like iced tea. I'm not sure what caused the problem in the pH... everything had been reading fine before the heater went out, but at least we have found a way to fix it.

Hope this info helps someone in the future!