Problem with hydroponic cucumbers

[mikey3030]

Hi. I'm new to hydroponics. This is my firat time growing cucumbers. I'm using flood and drain system. I'm using a 3 part nutrient solution by general hydroponics flora micro,grow and bloom. My light is a 250 watt medal halide. I am having a problem with my cucumber leaves spotting and rotting out. The lower older leaves are worse but it is also affecting the newer ones gradually. I flushed the system with fresh water for 3 days and the problem seemed to stay the same. 3 days ago I added the nutrient solution again and the problem started to get worse today. My ph is 5.98, ec 2.05 water temp is 72 degres. I am doing four feeds a day for 30 minutes each every 3 hours. My lights are now on at 5am and off at 5pm 12 hours. I added a humidifier because the humidity was low. My humidity now ranges from 40-50 percent. The temperature near the plants is 73 degres when the lights are on. The plants are producing a good amount of male flowers and so far only one female flower is starting to come out. Everything looks healthy except the leaves. Does anyone have ant suggestions to what is causing the leave problem and what it might be. Is it possible that the plants will produce heathy fruits? Thanks.