| It kinda depends on the method you are using. I use DWC a lot and just resupply what the plants use and NEVER change out the nutrient solution except as grizzman says -- when I switch out the plants. I grow indeterminate tomatoes mostly and some of them have been growing in the same little bucket for 3 years! I glue aluminum foil on the outside of the buckets to prevent light from forming algae. Some forms anyway, but it doesn't seem to hurt anything. I'm currently working on a ''shelter" which will house a row of 2-gallon plastic buckets in a wooden cave to prevent light from forming algae. The idea here is to have more room for the maters to spread out and grow more. I've up to now used the "single-truss" method of pruning the plants, but of late have decided to just let them grow like a massive monster. That will take more room than I have in my little greenhouse, so I've decided to move things outdoors and hence, the wooden cave idea. Each bucket has its own air pump, by the way. | 
