I just leave my tank alone.

I think nothing makes my heart sink more than that statement. People will then go on to say that they don’t do any cleaning, they only clean the filter when the flow slows to a stop, they top up the tank when the water drops. THey feed their fish and let the algae grow. They don’t test, or do water changes, and their fish are doing fine.


That word is a swear word now for me, but let’s be honest here. We deal with thousands of problems a year that our members have, and the vast majority of them come down to not doing water changes. I’ve been helping someone whose entire tank of fish was dying, and the next day he was on a thread telling a beginner not to bother with all that rubbish, his fish were fine. He’d just told me that they were all dead, and he was blaming poor quality fish from a large store. Fish he’d had 6 months. It was in no way his fault. So off he went to tell the world that no maintenance was the way to go.

Why water change.

You need to remove nitrates, remove hormones that fish produce and will out into the water, reduce the amount of pathogens in the water, and replenish the minerals in the water that fish and the cycle uses up.

What happens if you don’t water change?

Eventually dead fish, but the first things that start to happen is the cycle (the ammonia-nitrite-nitrate process) uses up the carbonates. Carbonates are what help hold your pH steady, no carbonates, and your pH goes down like an oily child down a slide, we call this a pH crash. Now your pH is low, too low for the organisms in your filter to do their job, or survive. We like our filter organisms, they keep our fish alive. Now your ammonia isn’t being changed into anything.

But there is an extra layer of biochemistry to consider, Low pH means that the ammonia is locked up as the safer, not safe, but safer, ammonium. So your fish won’t be doing great, but they will be surviving.

Until you have to do a water change. The carbonates will be replaced in the fresh water, and the ammonium will become ammonia, and that means dead fish.

Right so you’re now planning on not doing water changes. Well your fish will be in a living hell, but just as importantly that is warm, wet and a bacteria paradise, and some of those you can catch, and some are unpleasant at one end of the scale, and leathal at the other.

But I don’t need to clean out my filter

Quick question, do you flush the toilet, yes, so why don’t you clean out your filter, it’s not a magic box, it just catches and holds the solids, you need to take them out, Leave it too long and it will start to block up the mocroscopiic pores in your biomedia that houses the organisms you need in your filter. Also as all that stuff decays it will increase the nitrates in your tank.

But I’ve got a lot of plants.

Congratulations, i am a huge fan of plants, and there is no way that I can think of quickly where plants don’t help in a well stocked tank. But here’s the thing, they don’t help against those bacteria we were talking about, and plants thrive with fresh water as well.

I just don’t want to do water changes.

Fine, may i direct you towards a nice toy fish, or a screen saver.

What should I be doing?

Clean out your tank once a week. Take out 50% of the water and return water of the correct pH, KH etc to the tank. Remove the chlorine and chloramine some how, and clean your filter. Make sure the gravel isn’t building up gas pockets, and sit back and enjoy your aquaria.

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Ruth McDonald

Sailed twice around the world, started my acedemic career as an archaeologist and somehow ended up lecturing on science and researching fish.

Tropical Fish Keeping UK