Reef Aquarium Cycle

Simply put, biological waste (die off) turns into ammonia. Bacteria colonies will grow that consume the ammonia and turn it into nitrite. Both ammonia and nitrite are highly toxic and would kill most of the living creatures in your tank.

More bacteria colonies grow and consume the nitrite. It’s then turned into nitrate, a much less toxic substance. Your tank inhabitants can tolerate low levels of nitrate.

The science behind it is very complicated but you only need to understand the basics.

Your aquarium MUST go through this cycle before you add fish and/or corals. If you don’t wait for your tank to fully cycle, you will put the fish and corals in peril. Many, many people place fish/coral in their tanks too soon and end up killing them out of ignorance. This is cruel and totally preventable.

It usually takes from 3 to 5 weeks for your aquarium cycle to complete.

Cycling your reef aquarium is simple, but it does take time and patience.

If you haven’t read the Curing Live Rock section you should read it now. That section explains how you cure live rock and cycle at the same time. This is the simplest way to fully cycle your tank.

If for any reason you can’t cure the live rock in your tank, you will need an ammonia source to start the cycle. A popular choice is to buy one uncooked shrimp from the grocery store and bury it in the sand bed.

As it slowly decays, ammonia is produced and bacteria colonies start to develop. This is a slow process and will take 3 to 5 weeks to complete.

Water changes will only prolong your aquarium cycle, so please don’t do any during the cycling time. Just add enough fresh RO water to replace evaporation. Salt does not evaporate so don’t add any salt water.

I always recommend you run your skimmer, if you have one, throughout the cycling period.

Test for ammonia every 5 to 7 days. It will peak and then start to drop. After ammonia drops, nitrite will start to show up. Test for nitrite with the same frequency until it drops of. When both ammonia and nitrite test zero, your aquarium cycle is complete.

You can now start to slowly add the cleanup crew. If you add too many, too fast, the biological colonies cannot reproduce fast enough to convert the waste into nitrate. You can easily start another cycle all over again and probably kill the lives you just added.

Take your time. Nothing "good" happens fast in a reef aquarium. It happens slowly, by being patient. Bad things happen quickly and take a long time to turn around.