They could be rootbound, it's impossible to tell from those pictures. There's a troubleshooting form in my signature, get it filled and post the details in this thread to get more detailed advice into what might be causing your problems. Also, knowing your pH is important, so you'll need to find a way to at least get a good estimate. If you can't afford a pH pen, or one of the more accurate testers, at least try to get your hands on an aquarium pH kit to get a general idea.

Take care. :jointsmile: