Backyard Aquaponics
A place to discuss aquaponics

My AP system is 3 months old now and PH drops from 7.2 to 6.2.

Nitrate is around 100 ppm.

The new leaves seems ok but the old leaves start yellowing and dying.

While my lettuce plants are growing vertically.

Please advise on this issue.

growing vertically sounds like they don't have enough light or that perhaps it's the wrong season and they are bolting.. What light does the system get?

+1 Sounds like bolting.

The plants gets sunlight starting from morning till two o'clock PM. Yes, it seems like producing seeds. Is it because of the lack of sun ?

It's usually because of temperature. Lettuce is more of a cool season crop.