Discoloration on Rockwool

I recently plopped some seedlings into rockwool cubes, four to be exact. The cubes are 2x2 squares. I'm using a drip system with General Hydroponics Micro and Grow solutions, using the "general purpose - mild" mix recipe. This is all in hydroton pebbles under about 18000 lumens of cheap flouro light.

After the first day of reguar, timed watering I started noticing a slight darkening of the areas where the water drips onto the rockwool. I've now had the water going for about five days and the spots where the water hits the rockwool has turned a very dark brown. It's not slimy or sticky or anything; I'm not thinking it's algea (most of which tends to come up green anyway). I'm using the same nutrients, resivoir, lights, etc. that I've had for the past six months but I've never seen anything like this. About a month ago I uprooted my garden and cleaned all of my equipment with a mild bleach solution and it sat, dark and dry, for about two weeks before I set it all up again, so I can't see it being a fungus either. Then again, I'm no fungal expert so I couldn't say for sure. The seedlings seem fine thus far, and are rooting quite well.

Any ideas?

maybe the nutes didnt get mixed as well as usual
this happened to me when i started using organic fertz.
OK so far...

It's probably the micro coloring the dripping site. And you are not using the bloom? Seedlings and cuttings need P (phosphorus) to root, and that is in the Bloom component.

HTH

some of my nutes did that. If you're using Technaflora I think some of their early nutes do that. You can buy what are called Block Covers. They are just little plastic shields that prevent the light from reaching the sugars so the algae doesn't grow.

The algae isn't really a problem. But I SERIOUSLY fucked up my humidity for a few weeks in the early days. I got the rooms up to like 80% humidity(I had a bad humidity meter). Grey mold loves to eat algae and so I had to fight a bit of it off.

hi i got the same thing going on. so for me... no more top watering by hand... I flood my table and make sure the solution doesn't reach the top of my cubes.. but try to get the top as dry as possible so mold doesn't start to form or it will become a bigger problem.. i put out a thread out there because its new for me and very upsetting because the top of the cubes look like shit !!!!!!