help please?

Hi i've just recently started using hydro (90l nft) i'm not sure if this is a big problem or not but its very noticeable, after removing one of the cubes and the light being off for 2 days due to "unwanted attention". there is some what looks like mould started forming in the channels (where the opened space is) and around the tops of the remaining cubes (kinda dyed them from yellowish to green), how do i fix and prevent this happening again please help me and thank you for any advice

It might be residue from the water supply and not mold. It usually collects on the top of the rockwool cubes and on the top of hydroton etc. Most common when using town and city water supplies. If you're totally concerned post a pic. I usually clean it with a pump up sprayer. Use caution as seed plants will break more easier than clones when spraying with water.

It was collecting on the top of the cubes and, i forgot to cover the hole like i said when i removed one o the cubes and under where it should have sat on the nutrient channel started to go green in colour (Assuming is mold) same with top of cube just assuming its mold
lol, should i cover the space so that no light gets to the channel would that affect it?