help with snail aquariums

hi y'all! about 7 weeks ago i received some snail terrarium kits in the mail. generally, everythings fine, but some of the plants didnt fare well in the mail so i picked one up from my local aquarium supply store. a few problems have arisen. some context, i received two kits, both with practically the same setup but with diff size jars. i replaced the plant on the bigger one.

1: its been 7 weeks, and snail #1, in the smaller jar, has uh. eaten all of the leaves off of his plant. am i not feeding him enough? i give him a few flakes of fish food twice a week, and occasionally a bit of organic cucumber. is this just a thing with ramshorn snails, that you have to replace the plants every few months? i feel like thats not right

2: the bigger jars water is getting fairly murky. i don't really know what could have gone wrong here, since both jars are set up practically identical, but i don't know how to fix it. should i pull everything out and start over with new aquasoil/plant?

thank you so much... im so uninformed but hoping to get better :)