Brevin

I'd like to start by saying this a great forum and the information within has helped me immensely. I couldn't find an answer to my current problem, so I have to stop lurking.

I've been have weird brown water, that seems to be free floating diatom algae. Now from what I know, diatom algae only occurs in new tanks, however, I've had my tank for 3 years now as an established tank. I changed the lights to PC lighting 6 months ago and added pressurized CO2 via a glass diffuser around 3~4 months ago. I had problems with BGA, which a powerhead solved, with its increased circulation and regular dosing has thread algae virtually gone.

However, I still had diatom algae, the brown gunky stuff that you can get off your leaves fairly easily. The diatom algae even covered my thread algae, which created this fluffy, nasty thread algae. What I find interesting is that alot of the diatom algae is on the upper leaves and I've heard it prefers low light. So I upped my NO3 dosing to every day. However, that got my NO3 values to 80ppm quickly and one of my cories died. I went back to my original dosing thinking that after I got my algae crew that it would be beaten down.

Sometime around 2 weeks ago, I started getting an haziness in my tank. I was worried it was green water, but my tank turned a murky brown water. Almost like tannins, except I have no wood in there. I've tried, changing the lighting schedule, both longer and shorter. I've also changed the lighting intensity, but to no avail. I've also tried frequent water changes, but within 12 hrs it is brown again. It also seems to clear up in the middle of the night, almost like plants getting used to the light cycle, clearing up when there is no light and getting brown again in anticipation of the light in the morning.

I'll post a picture tonight when I get home.

Thanks,
Felix

My tank spec are below:
20 GallonH
Not sure of my CO2 levels, but my plants pearl well, and I have no more BGA. It is hard to test as my KH is 30 degrees. We have liquid rock here in Wisconsin.
8hr lighting with 55W; 2 hr with 33W
Dose EI:
every other day
2/8tsb KNO3
1/16 Mono potassium phosphate
1/8th Potassium Chloride
and
1/16 CSM+B on the off days.
and weekly water changes.