Frustration from past experiences has motivated for me to write an article about adding live things to your tank. I have lost a lot of money because I did not understand things about my tanks bio-load capacity. This article only applies to tanks that are already past their initial cycling phase.

Every tank has a bio-load capacity. The capacity varies based on several different things. It depends on the amount of sand/gravel, mechanical filtration, as well as other live items in the tank. Inside your sand bedare lots of little bacteria. These bacteria take care of the ammonia in the tank from things like fish poop. These bacteria also live deep in rocks where the current is low.

When you add live rock to your tank there is a considerable amount of matter that dies off. This matter produces ammonia. If you do not have enough bacteria in your tank, ammonia will take over and a mini-cycle can result. Live rock is only a problem when it is uncured. This can be avioded by only buying cured live rock. If it is uncured, let it cure in a seperate tank before you add it to your main tank.

The same thing happens when you add fish. The more fish you add, the more poop (ammonia) there is. Do you have enough bacteria in your sand bed and rocks to account for such an increase in ammonia? This depends on the volume of the tank, depth of sand bed, and amount of fish/rock you plan to add. There is no set formula (that I know of) to calculate how much you can add. This is where patience comes in. Here are some hypothetical situations:

1) Volume = 20 gallons

You want to add 10 lbs of live rock.  Go for it! Or No Way!

I would say No Way!  First of all, only having a 1 inch sand bed does no allow for a sufficient amount of bacteria. Adding 10 lbs of live rock will produce a considerable amount of ammonia from matter that dies off. Since the volume of water is so low, the water will have ammonia concentrations that will stress/kill your inhabitants. Most definitely a mini-cycle will occur. As far filtration goes, it is in the acceptable range. The main problem is that there is not a deep enough sand bed and rock for ammonia bacteria to grow.

2)  Volume = 80 gallons
DSB Depth = 3.5 inches
75 lbs of live rock
Filter rated for 800 gallons per hour

You want to add 2 lbs of live rock and a tang.  Go for it! Or No Way!

In this situation you would be ok. First, the sand bed is deep enough to house an acceptable amount of bacteria. In addition, having 75 lbs of live rock will house a significant amount of bacteria as well. 800 gallons per hour will definitely suck some of that ammonia producing matter out of the system. Adding only 2 lbs of rock wont produce enough ammonia to make your water unsafe due to ammonia. As for the tang, he will produce more ammonia but not enough to throw things off.

The ammonia levels rise when you add something to the tank. That is why you add things slowly and wait for everything to stabilize before you add more. This usually only happens if the rock is uncured. Uncured means it has not established any bacteria to fight ammonia. We recommend buying cured rock to avoid problems like these.