Topping up evaporation vs changing out water

I have seen a number of people comment or post about not doing water changes, rather just topping up evaporated water. Let’s analyze the two methods and explain why one is better than the other.

Standard water change method

See my post about water changes and amounts for full details, but essentially, water changes is a process that includes removing a percentage of the water from your tank. While doing so, you use a syphon or vacuum to clean up the waste and sediment from the bottom of the tank.

Topping up after evaporation

Aquarium tanks naturally loose water though evaporation, particularly if they don’t have lids. The top up method involves simply adding new water to the tank, without taking any out manually.

What’s the difference?

When evaporation occurs, all of the nutrients, minerals and heavy metal content that was dissolved into that evaporated water remains in the system. Over a period of time if you just top up evaporated water, those elements will accumulate and be in excess.

While certain ratios of minerals and trace elements are important to sustain appropriate biological functions, others effect the reproductive cycle of essential bacteria and microfauna, such as heavy metals.

The concentrations will over time become catastrophic when dosing fertilizers or relying on a water source known to contain a wide range of trace elements that come mains tap water.

Is there another way?

Yes, there is a half way point to this. A gravel vacuum that removes the sediment into a bag, will take out the trace elements and waste.

Doing this will allow you to clean the tank and not have to manually take out water.

However… you need to check your water when doing this. If your levels spike, you do need to manually take out water as well as vacuuming the bottom of the tank.