Setting up a saltwater tank and cycling process

by gerr Sun Nov 06, 2011 9:41 pm

Over the last year i have helped out a number of people setting up marine tanks and the same two questions were constantly asked. How long will the tank take to cycle? and How will i know when the tank is fully cycled?
The key to successful marine keeping is Patience and understanding how the biological system works also goes a long way.
To start with cycling a new marine tank you will need the following .....
RO (reverse osmosis) system or a lfs that will provide RO water
Bucket of marine salt
Powerhead
Heater
Ammonia, Nitrites, Nitrates test kits
Hydrometer or Refractormeter to test salinty

Fill your tank or container with RO water and maintain temp at 79 farnheit or 26 celsius. Add powerhead or pump into the tank to create a current and then add the salt in small amounts. Current in the water will help to break down and mix the salt alot quicker. Check the salinity of the water after 24 hrs and add salt if need be until the range is from 1.020 to 1.025 depending on if you are keeping fish only or a coral system. If the salinity is higher than 1.025 then saltwater needs to be taking out and replaced with RO water to decrease salinity. Just adding RO water will not bring down salinity.
tank is now full of water and its time for the next stage cycling the tank.

Ammonia

Ammonia needs to be present to begin a tank cycle. Best ways to introduce ammonia is by adding live rock to the tank as ammonia starts from the biological waste that comes from dead organisms decaying. Most live rock will have some form of dead matter on it. Another method is to add a frozen prawn to the tank and leave it to decay. Some people opt to sacrifice a fish as fish poo will kick start the cycle, down side of this method is that ammonia is highly toxic and will certainly kill the fish.
Ammonia level will rise before it starts to drop off.
Nitrifying bacteria will form and consume the ammonia and convert it into nitrites.
Ammonia level should not be detected in a fully cycled system

Nitrites
Nitrite level will rise to around 15ppm before it starts to drop off.
Again bacteria that forms on the rock and sand will consume the nitrites and convert them into nitrates.
Nitrite level should not be detected in a fully cycled system as it is also highly toxic.

Nitrates

Nitrates levels can be high in a newly cycled tank and if so large water changes helps to decrease the level. High level of nitrates will be tolerated by fish but will greatly effect corals. Also high levels will case the growth of unwanted algae.
There are different opinions on what level nitrates should be in a tank, some will say zero while others will say levels of up to 20ppm is acceptable. Personally i keep mine at 10ppm.

Time it takes to complete the cycle process can vary from tank to tank. The longer it is cycling for before introducing fish the better. Generally it is left for 6 to 8 weeks.
Test the water regularly during the cycle to see what phase the tank is at.

Biggest problem when the tank is cycled is people rushing out and buying loads of fish in one go. The waste from all those fish and the uneaten food will increase the bio load and a mini cycle can occur and cause ammonia and nitrites to spike causing a wipe out in the tank. Again Patience is the key and slowly introduce fish over the course of a few months.