Here's a new one to me. After my biweekly 50% water change the 125g turned coffee colored about 4 hours later. The next morning the tank was crystal clear as usual. The color was completely gone.

The fish where completely normal and showed no signs of I'll effects. In fact I keep having random danio babies appear. The gold barbs have also been spawning.

Next week I did a water change and the same thing happened. It's done it three weeks in a row. Just to see if it would repeat.

Tank has been setup and established for almost 4 years. Lowtech jungle with dry ferts. 230W CFL lights with no reflector so low par.
Builders sand and gravel substrate.


Any theories as to what this is?

I do a water change with a python and prime and add in dry ferts as I fill up the tank.

How many years you have your 125g up running? And how often you clean the filter?

I clean the filters around every six months or so. The generally don't really need it. I don't have much fish in the tank actually.

As I stated above it's been set up for almost 4 years (december).

It is typical old tank syndrome, tannins in the water gets locked in the substrate because the biomass buried within.

You should have a fairly low ph also, a water change the ph will temporarily higher towards the neutral, and tannins release(from substrate), a couple days later, ph will drop and tannis gets locked back in.

So either break the tank down and change the substrate or do a few two-a-day water changes get rid of some of the tannins?

Did another water change today all prepared to do another when the tank turned brown. Stayed crystal clear the rest of the day.....