Grow Mediums wilma feeding times

[Hydelane]

Hi everyone
looking for some advice please,I'm growing 4 autos in 11l Wilma system with coco, plants are now on there fourth week in the system and all is going well and they look great and starting their pre-flower stage.

I have up to now been feeding 3 times a day of 15 minutes but have started noticing that I am getting less run off, and my question thus is this indicating they are looking for another feed ?
this is my first grow in a Wilma so any advice would be great.

Thanks