The
Elodea crispa is actually
Lagarosiphon major and doesn't usually do too well in tropical tanks, it's more of a pond plant, it doesnt even always fare well in coldwater tanks.
The
Elodea densa is actually
Egeria densa, and this is an easy fast growing plant, however it does require decent light to grow properly, otherwise it rots at the bottom and will only grow floating up beside the lights.
I cant really see that well from the photo, but it looks like you may have planted them in bunches too. They require to be planted stem by stem each a few inches apart otherwise they will just rot at the bottom as the lower part of the plant receives very little light and oxygen.
To the right I can just make out a red leaved plant, that may be a plastic one. If it's not plastic, it's non-aquatic, most likely a
Hemigraphis exotica, I cant tell very well from the pic, but regardless its certainly not suited for your tank.
The plant in the front of the pic looks like an
Anubias sp., and should be tied to the rocks rather than planted in the sand, they often rot if planted in substrate improperly.
Your water looks very cloudy, which would suggest a bacterial bloom and possibly ammonia spike, have you tested the water recently? Ammonia in the water could be harming the plants and fish.
Also, you never mentioned what type and wattage of lighting the tank has, there's a good chance it's simply not suited for your plants

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Basically, I don't think there is a problem with your fish destroying the plants

.