The most important thing Ive learned from my time fixing hydro ops in warehouses is to block out all light from the solution.
If its just straight water, its not a problem.
But the moment you have anions (N, P) in water solution, any light hitting the water will start growing pathogenic microbes.
One year, I was called into a multi-warehouse op by the owner. The ‘master-grower’ had replaced the baskets in the Current Culture system with baskets from his home grow.
For months, they were battling toxic algae blooms.
I came in and saw the water right through the baskets and laughed.
To grow algae (cyanobacteria) you need water, nutrients, and light. Take away one of those and you wont get algae.