can i reuse my substrate and add some cocopeat to it?? and also if i reuse it without putting the cocopeat should i add more rotten wood in it?You could mix it in with your nutritious substrate as a base substrate, but the stuff has no nutrition value at all and is inedible. It won't ferment like the wood will, so I wouldn't try fermenting it. Honestly I'd just stick to a substrate of rotten wood an leaves.
i have try use potting soil but one of the larvae die few day later than i change back to the original substrate after i add some rotten woodWhy not use organic potting soil as a filler?
i put my 2 L3 allomyrino dichotomus in 1L box they have massive poop after just one week. Tq for the advise I think i will use the cocopeat for adult not larvaeNo, do not add coconut fiber. It isn't food for larvae and there's no point adding it. Imagine if someone put bits of glass in your food and you had to pick out the food from the glass in order to eat or eat it and hope it doesn't bother you. That's what it's like if you're adding a non-nutritious filler to the substrate.
If you get the right sized mesh, you can sift the larger pieces of poop out of substrate and then reuse what's left. Just add more rotten wood. If it's a rhinoceros or flower beetle, add old hardwood leaves as well.