As long as your root ball fits within the cup you are good. The great aspect of using net cups is that they allow the roots to grow outside of the cup which is great for aeration. If you are using net cups for flowering and your plant is going to end up taller than 24”, I’d use a 6” cup or larger.
One method is to use plastic sheet covers. This is an easy solution if you are having an algae problem. The coco coir rolls work great in trays. The coir mats are reusable if you clean them. If you are worried about the algae right now, relax, it does not usually create a huge problem. If you do want to clean it use a tablespoon of 35% hydrogen peroxide in a gallon of water. Fill a spray bottle and spray the tray (its fine if the plants are in it).
I hand water my plants and I have to water too often. What can I do so I do not have to water as often?
Coco coir is a heavy water retaining media. If you use guano top dressing it will create a vapor barrier that will slow the top of the soil from drying out in the pot. You can also use vermiculite and peat moss for the same effect.
Not really. One method of curing this is to use plastic sheet covers; this is an easy solution if you are having an algae problem. The coco coir rolls work great in trays. The coir mats are reusable if you clean them. If you are worried about the algae right now just relax, it does not usually create a huge problem; but if you want to clean it immediately, use a tablespoon of 35% hydrogen peroxide in a gallon of water. Fill a spray bottle with the solution and spray the tray (it’s fine if the plants are in it).
Soap and water is fine. Some people use prefer to use water that has pH down mixed in it. Warm water will dissolve solids more easily.
It changes with system type. NFT and DWC systems are exceptions to the rule since their roots extend and survive beyond the root ball (within the system). Here is the rule. For every 1 foot you expect your plant to be when it is finished growing, you will need about 1 gallon of media. Rockwool needs a bit less area, because the density of the media allows more root growth in the same size container. Most people start out with a smaller container and transplant up one or two sizes during the growth cycle although it’s best to keep your plant in the same container the whole way through if possible. Less transplanting equals less shock and trauma, and less to go wrong. Also, if the plant is in a large container to begin with, it will actually grow faster because the roots will not bind up as quickly.