one of my fish keeps getting constipated. i gave him a diet of frozen peas for over two weeks and he was doing well. soon after he went back to goldfish crisps the problem came back. i also feed them bloodworms occassionally. i've repeated the frozen pea diet (with a little epsom salt mixed in) a couple of times. do i need to switch food or is there a better way to prevent this from reoccurring?