You have bought yourself a new aquarium, filled it up with water, then added a few fish, and naturally you feed them. The fish digest the food and excrete waste into the water…

In nature fishes live in vast water bodies or in flowing rivers that refresh their water continuously removing waste. But in the stagnant and limited quantity of water in your aquarium the nitrogenous waste products break down into ammonia. Within a day the ammonia reaches poisonous levels in the aquarium. Your see your fish scratching themselves.. within a few days the fish look sick.. by a week the fish are dying.. you blame the local aquarium shop for the unhealthy fish and go buy some more.. the local aquarium shop owner suggests that you clean the tank and try again.. and the deathly cycle begins again.

You have to allow the nitrification or nitrogen cycle to establish itself in your aquarium. In this cycle of events the waste decaying matter is converted to less harmful chemicals which your fish can tolerate and plants can utilise.

The nitrogen cycle explained:

When the ammonia levels in your new aquarium reach a certain level (after a few days) nitrosomonas species of bacteria from the air settle in the water and start to form colonies in your filter or sand. These bacteria convert the ammonia (NH3) to nitrites (NO2-). The ammonia levels drop and the nitrite levels start to increase. The nitrites in the water are also toxic to fish, so your aquarium is not ready as yet..

When the nitrite level in the water has reached suitable levels another bacteria of Nitrobacter species starts to establish colonies in your aquarium. These bacteria convert the nitrites to nitrates (NO3-), which are less harmful in small quantities and are absorbed by plants or algae.

Now the aquarium is truly ready to host aquatic life. This process takes anywhere from 3 to 6 weeks depending on water temperature. One of the indicators of an almost complete cycle is visible algae on the glass.

The process looks like this : Ammonia ->> Nitrite ->> Nitrate

How to speed up the nitrogen cycle:

The beneficial bacteria multiply slowly, so to speed up the nitrogen cycle you can introduce these bacteria into your aquarium in large quantities. The best way to do this is by borrowing some from an aquarium that is already established. An established tank would be one that is at least 3 months old after it has been set up or cleaned. You could:

1. Take a cup of sand from this established aquarium and add it to yours.
2. Put a cup of this sand in your filter temporarily.
3. Borrow a filter from an established tank and run it in your tank for a few days.
4. Squeeze the water out of a filter media of an established aquarium.
5. Fill your aquarium with water taken from an established (larger) aquarium.

Taking care of the beneficial bacteria:

NEVER totally wash and clean an established aquarium if possible. However if you have to do so, try the following procedure, which will save your colony of beneficial bacteria from destruction:

1. Siphon out all the water, filter the water and save for later.
2. Remove the filter and keep it wet in this water.
3. Do not clean the filter.
4. Remove the sand, rinse, filter the water and save this water as in (1)
5. Now wash tank, substrate (sand), stones etc.
6. After you reset the tank, pour back the water saved in steps 1 & 4
7. Put back the filter without cleaning.
8. Change water after a few weeks.

NEVER add medication directly to your aquarium unless it is from a reputed manufacturer and the package clearly states that the medication is harmless to filtration bacteria and plants.

NEVER add antibiotics like tetracycline to the aquarium. Treat fish with antibiotics in a bucket of water or separate tank. Antibiotic and other microbicidal chemicals (betadine) will kill all the beneficial bacteria along with whatever infection you are treating.

NEVER clean out a filter media (sponge) completely. Rinse the filter media gently in clean water to remove surface blockage and re-install. This will retain most of the beneficial bacteria.

NEVER add chlorinated water directly to your aquarium. Chlorine is added to water to kill harmful bacteria, but it also kills beneficial bacteria very effectively. Use a chlorine remover, or allow water to sit in a bucket with an aerator for some time before adding it to your aquarium. Water stored in a sump or overhead tank will lose all chlorine over time.

And note:

NEVER add a lot of new fish to your tank in one go. The bacteria colony will not be able to handle the sudden increase in load. Buy and add new fish one pair at a time. Now you know why fish suddenly start dying after you have added a new lot of new fish.

NEVER increase the feed amount to the fish suddenly - the bacteria might not be able to take the extra load of excrement.

To prevent overfeeding when you are leaving town for a few days, put the daily feed amount in small packets with instructions to the person who is looking after your fish.

My fish are already dying, what do I do ?

Reduce the levels of these toxic chemicals by a DAILY partial water change. Alternatively you could remove the fish and put them into a large bucket of fresh water immediately. Replace the water in the bucket completely every day till the aquarium has completed the nitrogen cycle.

by Rajendra Kumar, G.G.
First published in "Infoaquaria", newsletter of The Aquarist Society of Karnataka, India
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