Green Water - Again- I'm at a loss

[evercl92]

We'll start with good news - GDA hasn't reappeared. Bad news, green water has appeared. It started 2 weeks ago, out of nowhere. So, wanting to get a jump on it, I did a 3-day blackout. Crystal clear water after that. Four or five days later, started coming back.

Yesterday's testing:
pH 6.6
kh 5.5
nitrate 10
phos 1.5
ammonia 0

I typically dose 1/2 tsp CSM+B 3x/wk, 1/2 tsp K2SO4 3x/wk, and dose KNO3 and KH2PO4 to get levels of 20-30ppm and 1-2ppm respectively. Pressurized CO2 at about 4b/s, 130wt of CF lighting is on 10hrs, with another 260wt CF lighting on for 9hrs (starts 30min after first set, ends 30mins before first set). Tank is a standard 120gal, 4ft x 2ft x 2ft. I use the 50 micron version of these in my HOB filter, and it seems to do a pretty decent job. When I clean them, they (recently) have had a slightly green color and smelled like algae. So it seems to be filtering some of the algae out.

Previous threads indicated that increased ammonia levels are to blame, but all fish are accounted for and I've done no recent changes.

Obvious solutions are UV sterilizer or diatom filter. I'm looking to see if anyone can give insight into a reason behind why this is occurring so that the issue can be fixed at the source.

TIA

 

[Purrbox]

It sounds like you never completely got rid of the Green Water. The fact that your filter pads are still green when cleaned seems to indicate that there's been a small amount that never went away even though you couldn't see it. Often a 3 day blackout isn't long enough to get rid of Green Water and other algae, so you may need to try a longer blackout.