the reason a 40 gallon plus is recomended is because the bigger the tank allows for a little more mistakes. Not a whole lot but they can be a little more forgiving. You should be able to go with the 30 gallon though but keep an eye on it as far as water parameters go. Are your ammonia and nitrite at 0? they are the toxic parts of the cycle. Also you said you did a 30% water change that might have been a little to much for the tank you should not really go over 25% at a time unless its a real dire emergency you might have tossed the tank back into a mini cycle. If by chance thats what happened let your water straighten back out before adding anything else. Everyone has there own preferences as far as water changes, additives and everything else but each tank is different you just have to find what works best for the tank itself. But for a suggestion after the cycle is done ya might try 10% every week or every other week, i have a 30 gallon eel tank that this works great on so give that a shot. _________ karla  75 gall, 80 lbs sand, 110 lb lr, 10k pcs, atinics, emperor 400, prizm skimmer, hagen and maxi jet powerheads | 
