I'm guessing that something is off. I've not experienced aquaponics, but long spindly plants IMO are telling you that they aren't getting enough light or nutrient. How are their leaves looking? big and lush, or on the small side? If they are big and lush, you could have too much nitrogen, but I doubt that is the case. So, I go with light or not enough nutrient. Magnesium is great for improving plant vigor. You can do a foliar spray. I'd do a bit of research, but, I think you can do it every 2 weeks. If I were in your place, I might try a foliar spray of epsom salts and miracle grow. I know we're all trying to be as natural as possible, but IMO, what good is natural if we don't have the produce to show for it? I just gave my garden a good hosing with miracle grow, and followed that with side dressing of 10-10-10. My garden was looking noticeably better within 24 hours!