What are the "3 leaves"? The third set of leaves? How old is your plant(s)?
the 3 leaves are right above the round leafs right above those are the 5 leaves.
Depends on what leaves you are talking about and the overall appearance of your plants. If the leaves are curling in and/or drooping but still green (not yellow or brown or drying out) then your plant MIGHT be drowning, and this might be because...
Sounds like you might possibly have a bacterial or algae infestation in your root zone. These nasties thrive in low dissolved oxygen (DO) conditions. The roots don't, and the plant often takes on an over-watered look.
If you decide this is your problem, then you should consider doing two things in my opinion: 1) treat the infestation; and 2) takes steps to prevent it from happening again.
First, in order to try to eliminate the nasties you'll will want to completely clean out your system. You should remove each plant and rinse off the roots. You should trim off any dead roots or damaged roots. Dip the roots in a hydrogen peroxide solution 1/4 to 1/2 cup of 3% H2O2 per gallon of water, depending on how mature the plants are.
You should then clean your entire system using a strong bleach or h202 solution. Make sure you rinse everything really good before putting the plants back in.
Second, in order to insure you don't have a recurrence you should take some preventative measures. Make sure you're reservoir is light-tight; algae can't grow without light. Try to keep your reservoir temperature down (below 75* F; below 70* is better); high water temp means lower DO and higher risk of infestation.
If you can't keep the temperature down, then you should consider adding a more powerful air pump or another airstone, and treating the water to help prevent reinfestation. The best way, in my opinion, to treat the water is with H2O2 - UNLESS you are using organic nutes. H2O2 will both kill the nasties and increase the DO in the water.
If you're using chemical nutrients then the idea is to maintain a sterile environment. Go with a lower nute concentration mixed with 2 tablespoons of 3% H2O2 per gallon. The H2O2 dissipates, so you'll have to add some back with your top-off water. You'll probably have to do this the entire grow.
Hope this helps...