Fish in cycling, a beginner’s guide.
This is the process of cycling a tank using fish. Most people on the forum advise against this, but since so many of us fall into the trap of purchasing fish a few days after setting up the tank on their LFS’s advise, I thought I would write this guide. If you have not yet added any fish, I would strongly advise you to look at this thread, here to fishless cycle your tank. This is far more humane for you fish.
What is cycling?
This is the process of building up a colony of filter bacteria, to break down your fishes waste. Your filter will not function correctly until the cycle has finished, and unless care is taken, your fish may get poisoned to death as a result It is important to maintain this colony of bacteria at all times, as your fishes health depends upon a correctly working filter. Please read-up on filter media, here and also general maintenance, here
In a cycled tank, ammonia from fish waste is broken down into nitrite, by one set of bacteria. Another type of bacteria then breaks down nitrite into nitrate, the usual bi-product of your filters.
The term “Cycling” came about, as this is the process of establishing the nitrogen cycle in your aquarium. Fish produce waste. Some in the form of ammonia and other waste in other forms, which are converted to ammonia. There is one set of bacteria that break ammonia down into nitrite. Then another set of bacteria break this down into nitrate. In nature another set of bacteria would break nitrate down into nitrogen gas, and oxygen. This does sometimes occur in the aquarium, but filters are designed to stop this. This is because the by-product of the nitrate breakdown phase is Hydrogen Sulphide, which is also toxic. If enough Hydrogen Sulphide gets released, it can crash a tank (indirectly) by removing all the Oxygen from the water. This is why a tank ideally only contains bacteria to break down ammonia and nitrite.
How to cycle with fish in your tank
As above, we are trying to build up a colony of bacteria, to remove your fish’s waste. To do this with fish in the tank, however, we will be exposing them to poisons, mainly ammonia and nitrite (note spelling), which will eventually be converted into nitrate, the by-product of your filter. It is important for your fish’s health, that the ammonia and nitrite levels remain low. These two chemicals are dangerous long-term at any level detectable, but start showing short-term damage above 0.25mg/l, or 0.25ppm. Invest in a test kit, to monitor these readings. Nitrate is also toxic in large amounts. 50ppm should be the highest you allow nitrate to go, but fish will adapt to values up to 100ppm. Liquid drop tests are the most accurate, and dip strips are notoriously inaccurate. I use the Tetra range of test kits, but many on here recommend API. An API master kit will cost around £25, and Tetra are more expensive. API is not available to me however, and this is why I use Tetra.
To keep the ammonia and nitrite at an acceptable level, we must water test at least twice a day, and carry out 50% water changes as appropriate, i.e. if any reading for ammonia or nitrite comes out above 0.25. Testing needs to be done regularly, as conditions in a cycling tank change quickly. It isn't uncommon to go from ammonia only, into a phase where ammonia is undetectable, and nitrite is through the roof with this type of cycling. To keep our fish alive, we must monitor values of ammonia and nitrite carefully, or we may seriously damage our new pets. All water added to a tank must be de-chlorinated, or the new water may kill either the fish or the filter media’s bacteria. Tap water conditioner is used for de-chlorinating new water. There are many brands out there, mostly doing the same job. Check they remove chlorine, chloramines and heavy metals.
A pH below 6 will dramatically slow the cycle. If it drops below this, carry out a water change. pH is a measure of how acid or alkaline water is, and is held stable by minerals dissolved in your water. A stable pH is more important than one in the ideal range, unless your pH repeatedly drops below 6. If the pH repeatedly drops, you are short of minerals in your tap water. You can add coral sand or coral gravel to the filter or substrate to up the hardness of your water, and raise the pH. This will hold the pH stable at this new value, unlike many other chemicals. Make sure you add this slowly, until the pH reaches 7. Adding too fast will stress your fish.
Once levels for ammonia and nitrite have been 0 and nitrate has been rising, you are cycled for that fish load, and you are ready for a few more fish, space allowing. Remember never to add enough fish to double the numbers in a 24 hour time period. This is because it will take time for the existing bacteria to multiply sufficiently to allow for the increased load. Always test the water before adding fish, and also test around 12hours after, to ensure all levels are at a safe value. Check all levels daily for a week after adding fish, to ensure the filters are still coping Once cycled, and all levels for ammonia and nitrite are nil for a week, and nitrate is steadily rising, get yourself into the usual weekly maintenance routine, as described in the articles linked above.
Any suggestions for improvement welcome
Edited by eaglesaquarium, 17 July 2013 - 06:43 PM.