5 X 20gal. "plant only" tank system

For automation on fertilizing, one idea I thought of was to use an electronic fish feeder, the kind where you put in the food in each compartment and each day it tips it over into the water. I have no idea if it would work for fertilizers or not but it might be worth a shot.

 

1. Filtration is important in a plants only tank because cleanliness is an attribute when you are trying to avoid algae. Cannister filters especially are also good for adding more water circulation, and good circulation is also an attribute when trying to avoid algae.
3. Use individual tank CO2 injection. It is hard enough to maintain adequate and consistent CO2 concentration in a single tank, without complicating it more by trying to get the concentration needed by 5 tanks to be the same. You can use a single CO2 cylinder, and single regulator, but use a manifold with individual needle valves, check valves and bubble counters for each tank.
4. You can grow plants very well with either an inert substrate as simple as pool filter sand or a nutrient rich substrate such as ADA Aquasoil. You just adjust the fertilizing method, and other maintenance to complement the substrate you use.
5. Water changes do two important things, in my opinion. They allow you to discard water that has built up contaminants or excessive fertilizers before any problems can occur. And, they give you a good opportunity for tank maintenance, keeping the plants well pruned and the tank and substrate clean. So, any permanent plumbing you can install that makes water changes easy to do is a major advantage. Ideally you will do a water change by just opening one valve to drain off the existing water, and opening another valve to refill the tank.