do water changes matter?

[romsoccer12]

im not going to lie, im lazy. I hate doing water changes. Theyre a pain. I put in 1 gallon of RO water every week from evaporation. Could this replace water changes? My friend who has a nanocube has never done a water change and its been probably a year or 2 and it looks great. I know there are good reasons to do a water change like for a spike of ammonia or nitrate or somthing but is it necessary if nothing bad is happening?

[der_wille_zur_macht]

This is a loaded question.

First, some basic theory:

Saltwater is a complicated solution containing dozens of compounds in exact proporations. When you started your tank, you mixed a salt mix with water to create saltwater. This "new" saltwater was more or less close to ideal, in terms of the chemical composition.

A typical modern reef aquarium has a pretty high biomass - the livestock we typically think about (fish, corals, etc) plus lots and lots of other life - algae, bacteria, pods, worms, etc. As all of these life forms go on living, they perform various biological processes. Some of these processes use up the good chemicals in your water, some processes dump bad chemicals into the water column. The end result is that, over time, your tank's water is depleted in terms of good chemicals, and gets loaded up with bad chemicals.

The most straightforward way to handle this is a water change. You mix new salt mix with new water and replace some of the tank water with the new mix. This helps re-establish the correct balance of chemicals. However, it should hopefully be clear by this point that we're not really concerned about changing the "water" (i.e. H2O) itself - rather, we're interested in changing the different chemicals dissolved in the water. Since it's extremely difficult or impossible to extract specific ions from the water column, it's easier to just replace the solution rather than target specific chemical compounds.

Let's tackle a few specific points you're making:

1) Topping off the tank for evaporation can NOT replace water changes. When you top off, you are (hopefully) adding 100% pure H20. As described above, it's not really the WATER we're concerned about, it's all the stuff dissolved in the water. Topping off with fresh water does nothing to re-balance the various chemicals in solution in your tank.

2) Your friend is an example of a lucky person who has managed to be successful desipite not following commno best practice in the hobby. Surely, it is very possible to be successful without water changes. It's also possible to be successful with tap water instead of RO/DI, but for the vast majority of hobbyists, and the vast majority of tanks, water changes are a part of life. They are more or less foolproof, and though perhaps the average approach to water changes is a bit overkill, it's probably better to err on the side of caution in a matter like this.

3) Water changes for ammonia or nitrate spikes are appropriate. This is an example when you might choose to do a change based on something you observe in the tank. However, there are dozens (if not hundreds) of chemicals in solution in your tank that are very difficult or impossible to measure or test for. Any one of these compounds might be crucial to the life in your tank. Since it would be more or less impossible to monitor and adjust every single one of these parameters, it's far easier to just do regular water changes.

[romsoccer12]

thx that helped a lot

[Michael]

yep great post