Have used flood and drain for decades , hydrocorn or granit 3/8.
When you plant your plants put black plastic over the exposed roots and rocks/rockwool. This stops the groth of stuff. Plus it keeps the RH lower and you use less water.
I use thick trash industrial bags for the home supply.
With the exposed area of 32 4.5 gallon buckets , that a lot of area.
Note my tank is also light tight to prevent light from getting in the resivore.
On you next grow bleach the hell out of things and start with a algie free system