This is a hard question to answer because I don't know the history of your hydroponics
greenhouse garden. When was the last time you cleaned and/or replaced the solution?
You should also make sure your solution is circulating properly and doesn't have any debris such as odd bits of plants, or fragments of the media in it blocking circulation.
You should also test the pH of the solution. When plants go through fast growth, particularly just before maturity, they give off more wastes. This over-saturation of wastes raises the acidity in the solution. So either replace it completely if the acidity is too high OR dilute it down with water.
greenhouse hydroponics are really easily subjected to parasite infestations which do respond well to vinegar treatment.
Also, did you flush the system and clean it well between crops? If you empty the beds, dump the solution, and flush out the pipes, trays and medium, you can go ahead and do it with a 1:5 ratio of vinegar:water. Very simple but effective.
If you could give more information, perhaps I could be more helpful!
Merme