Originally Posted by MsRobin
It's going to be both we've put about five pounds of live rock in the tank to start out with and two striped cardinal fish to start the process, purple alge from the Rock has already started to grow a little into the sand and the fish haven't seemed to be changed by that.. But I've been checking all the levels and nothings really changed from when we started.. Thanks for the advice of the canister ill definitely clean it at least once a week or more. If there's anything else I should know.. Let me know thanks :)
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I would put at least ninety pounds of live rock in the tank. Your biggest forms of filtration in a marine tank are: Live Rock, Live Sand and a Protein Skimmer. Aerobic (oxygen feeding) bacteria present in the Live Rock convert Nitrites to Nitrates and anaerobic (low-oxygen feeding) bacteria present deeper in the Live Rock convert Nitrates to Nitrogen Gas (which leaves the system naturally).
Since you have a mix of crushed coral and regular sand, I will not get into Deep Sand Beds and their benefit in home aquaria. I do not reccommend you converting what you have into a Deep Sand Bed, because the crushed coral will be detrimental to the function of the sand bed. If you want to read up on Sand Beds and their denitrifying abilities, here is an article: Ron Shimek - Deep Sand Beds
Badx is right, you need a good light and a good skimmer to keep coral. You also need to make sure that Calcium and Alkalinity levels stay within their respective "safe zones": Calcium needs to be 400-450 ppm and Alkalinity needs to be 8-12 dKH. Because Nitrates have a direct effect on the reduction of Alkalinity in a home aquarium, you need to make sure you have a good skimmer since you do not have the benefit of a denitrifying sand bed.
I personally run a 4" Deep Sand Bed, 25 lbs of Live Rock and a Prizm Skimmer (I am not as worried about the skimmer since I rely on my sand bed to do all the work of denitrification) in my 20 gallon. I use a 30w LED light (that can be a little "spotlighty"), a 100w heater and two 240gph powerheads. I just started stocking this tank, have crabs and snails in it now and am putting two clowns and a goby in this weekend. I like to run a tank empty for a month before adding fish, as to make sure that my Alkalinity and Calcium levels stay consistent and my dosing schedule becomes regular. I know that adding fish will change the dosing schedule, but I don't run the protein skimmer until a few weeks after I add fish so that it has something to skim.