Water Flow Strong Enough ?

[psycho-killer]

hi there,

i have a 18 gallon tank,im running a Canister filter of 1200 Litres per hour is that strong enough ? the filter blows down the lengt at the back of tank ? will that bother fish? it makes a whirl effect on the top of the water should i maybe place a live rock at the end of the tank so the water flows through the rock ?

i have added nitrivac hope that wasnt a stupid idea, they say it breakes down the ammonia and nitrites a little faster and my ammonia after 2 days went down quite a bit,i also removed the filter media and running my filter empty. getting more live rock this weekend about 6 kg. i want to see if i can get hermit grabs and snails as well,hope my cycle is finished within 32 hours.. my current live rock is starting to get browish and there is slippery algae forming in the corner of my tank and just behind the filter and alot of see through worm type thingies,swaying at the moting of the water on the rocks..

thanks for the help,

starting a 5 gallon tanks as well...