Water changes

According to many sources the time to change the water is when the nitrates get high.

My parameters barely change, they are always zero except trace nitrates at most. My 20long is a little overstocked, I have 18 tetras, mostly neons but 2 glo tetras. It was only supposed to be 15 neons but I combined the ones in the 10 gallon that also has my Betta because his fins grew longer and I felt they would be too much of a temptation for the ones in with him.

Yet still, my parameters in the 20 are pretty stable. I have been doing a 3 or 4 gallon change and gravel vacuuming about every 5 days, because the fish poop and the hornwort sheds. At the moment they are happy and healthy and I want to keep them that way.

I kind of expected a few to die, I did lose one the first week but none after that. I had some ghost shrimp as cleaner uppers but that didn't work out that well.

I think I have too many neons to consider a clean up crew so my plan is to do water changes at more frequent intervals. I thought I would get some other opinions or options.

At any rate, the neons are striking when they shoal together. Here's a pic of the tank.

Personally I like to change the water on a schedule 50% weekly so that the nitrates do not get a chance to build up. Be aware that the liquid Nitrate test kits, API etc, one of the reagents has to be heavily shaken otherwise it doesn't show the nitrates. A light shaking will not do. I mention this because I had a test kit that even with 100 ppm nitrate solution it would not register more than 5 ppm. Typically the liquid test kits seem to be more accurate in spite of the need to shake issue.

Also consider that other materials/chemicals build up in the water that we do not test for, but may affect the fish.

You do water changes for 2 main reasons.
1) to reduce nutrients like ammonia, nitrite & nitrate.
2) to dilute disease organisms in the water.

Fish live in a soup of microscopic organisms including bacteria, fungus, viruses, protozoans, worms, flukes and various other things that make your skin crawl. Doing a big water change and gravel cleaning the substrate on a regular basis will dilute these organisms and reduce their numbers in the water, thus making it a safer and healthier environment for the fish.

If you do a 25% water change each week you leave behind 75% of the bad stuff in the water.
If you do a 50% water change each week you leave behind 50% of the bad stuff in the water.
If you do a 75% water change each week you leave behind 25% of the bad stuff in the water.

Imagine living in your house with no windows, doors, toilet, bathroom or anything. You eat and poop in the environment and have no clean air. Eventually you end up living in your own filth, which would probably be made worse by you throwing up due to the smell. You would get sick very quickly and probably die unless someone came to clean up regularly and open the place up to let in fresh air.

Fish live in their own waste. Their tank and filter is full of fish poop. The water they breath is filtered through fish poop. Cleaning filters, gravel and doing big regular water changes, removes a lot of this poop and harmful micro-organisms, and makes the environment cleaner and healthier for the fish.

Fish also excrete/secrete other things besides ammonia, things we can't test for. These also build up in the water and are removed by water changes.

Here's a good article on the subject: http://advancedaquariumconcepts.com/water-changes-and-water-quality-in-aquariums/

IMO, WC's are the single most important thing we need to consider, if we choose to keep fish.

We have an article here on TFF that explains the reasoning behind water changes.