1. What kind of system do you have, what stage of growth are the plants in, and what is being grown?
2. What is your environment? Classroom? Trailer? Home schooling? What are your current ambient temps?
3. What kind of nutrients are you using, what is being grown, how old are the plants, and what kind of system do you have?

Is this a true hydroponic system you are using? Or have you just thrown a bunch of plants into rockwool? Details would help with helping you. Otherwise, I have yet to meet a psychic around here. :-) Regards. -v

Hi Duncanvillehigh,

This sounds a bit like a school?
I do not what type of hydroponic setup you have, but if you are receptive to new ideas, please have a look at my web site from Australia, below.

It gives ALL details needed to make your own system, your own nutrients from basic chemicals, how to adjust nutrients, hints for success, an FAQ page and links to other sites, none of which seem to use sand. Sand is cheap, and it supports roots properly, and your pump needs to run less than 30 minutes per day.

Save each page as its own name into one directory on your computer, and you can navigate from one to the other when you are off-line, and it will feel as though you are still on-line.

Cheers,
Jimr007
Sunshine Coast
Queensland
Australia.

Here is a link that might be useful: Simple Sand Hydroponics