Sounds like overwatering and likely in too small of a pot. Possible underfeeding or ph out of range. But filling-out the troubleshooting form (copy-n-paste the appropriate form here) will help with a diagnosis rather than a guess. (the link is in my signature)

One good dose, or repeated smaller doses of H2O2 will kill the beneficial bacteria in the soil. That's not a good thing to do. How about we find out what's going on and fix the problem rather than mask the symptoms...? :thumbsup: