Cloudy white water - bacterial bloom explained

A common situation that my customers face with new aquariums (and, of course in established aquariums) is bacterial blooms - the cause of cloudy white water in an aquarium.
In new and established aquariums this is the result of waste products being broken down by bacteria  and, a spike in ammonium following.

There can be many causes for this.... in a new aquarium it can be a result of excess nutrients in the water. This results in certain types bacteria multiplying in huge numbers to breakdown the waste causing a milky white effect in the water. The bacteria will eventually die off as a result of starvation when their nutrients in the water decrease i.e. there is less food for them to eat. An ammonium spike usually follows the appearance of this cloudy white water followed by the next group of bacteria that grow and breakdown the ammonium. Once the full cycle is complete i.e. ammonium --> nitrite --> nitrate you will notice that on your water test kit no longer registers ammonium or nitrite and, but registers nitrate in your water.

In cycled aquariums bacteria blooms can be caused by overfeeding or washing the aquarium filter with fresh tap water which contains chlorine - killing the colonies of established bacteria in your filter resulting in a reset of the bacterial cycle therefore, a bacterial bloom.

If this were to happen the best thing to do is to make sure your air stone is on full ball and your water surface agitation is at its maximum. Fish will usually survive this event in a freshwater tank.... but, probably not a saltwater tank. Its best to try to avoid resetting your aquarium cycle as this causes stress to your fish and often results in diseases such as white spot.

When first starting in the aquarium hobby (about 10 years ago) I went through the stress of bacterial blooms and associated ammonia spikes a number of times. At one stage I owned a 3 foot saltwater tank with a canister filter and about 10 kg's of live rock, a pyjama cod and a lion fish (although i had no idea about their ferocious eating habits - which I was unequipped for). As many new marine hobbyists do I fed them way too much and, as a result caused a bacterial bloom and a huge ammonium spike! Needless to say this killed both my fish ... due to my impatience..... the tank was only 1 month old and deciding to add these two hungry beasts into my aquarium was not a wise choice. The bacterial colonies in the tank and filter were not established yet.... well not enough to handle the these fish and their waste.

As if this experience wasn't enough I tried again i.e. got rid of these dead fish let the tank cycle again and, then added a few corals (not such a bad idea). However, I made the unwise choice of adding liquid coral food and more than likely overdosed the system. Next morning I woke to find that the aquarium had turned cloudy white again! and, that all the live rock had died off.... the tank had a putrid smell. Besides overfeeding.... in hindsight the canister filter probably wasn't the best choice for this aquarium.

When first starting in the hobby most people do not realise how much work is involved with setting up an freshwater or saltwater aquarium.

So more often than not bacterial blooms will resolve themselves however, 25% water changes don't hurt and, holding off of feeding your fish is probably a good idea also.

Dan