Small Orginisms in Water

I flood a 4 x 4 tray mixed with 75/25 of hydroton and small rockwool cubes. The cubes on turn that get direct sun light seem to get kind of moldy and now there seem to be extremely small orginism like creatures in the tray when it floods but it seems there missing from the resivoir so i think they live in the moldy cubes? Please help are these bug things harmful.

All bugs living in your cubes or water are bad, they are probably eating your roots.

Sounds like fungus gnats, What do the look like, Are they small white bugs about half the size of a grain of rice?

They are probably smaller than half a grain of rice but yes they are white, how do u get rid of fungus gnats?

Treat your rez with a strong dose of h2o2 and cover your media with a Light Barrier.

should i run the water through the tray aswell or may that hurt the plants