Is water top up after evaporation okay?

[kevfiz]

Is it okay to top up the tank with a bucket of water after evaporation rather than water changes? I have been doing this for a few months now and noticed next to no algae now and have not lost one fish since.

 

[Byron]

The answer as to whether or not it is safe depends upon your water parameters. If the water is on the hard side, the evaporating water leaves behind the salts (mineral salts, like calcium) and these can increase to problem levels, again depending on the GH.

With respect to water changes, these are essential regardless. A water change is the only way to remove pollutants that build up and cannot ever be removed by any filtration. Plants can help, but not when the fish load is like it is in any of our aquaria. Regular (once a week) water changes removing a decent amount of water (50-70%) is recommended for healthy fish.

You should not lose fish in either case, though that does not mean they are not being impacted...they are if water is not being changed regularly.

Regular Partial Water Changes

Byron Hosking November, 2010 (rev April 2021) Nothing is more important when it comes to aquarium maintenance than regular partial water changes. The adage “an ounce of prevention is worth a pound of cure” certainly applies here. One frequently reads of products that will reduce the need for...

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[kevfiz]

Water change it is tomorrow then

 

[StripySnailGirl04]

Hmmm, your water shouldnt evaporate to such a massive amount that you need to add water. Probably almost harmless to do but does your tank have a lid? How much has your water evaporated?

 

[GaryE]

Minerals stay in the water, as do impurities and pollution. They don't evaporate. So as you go along your water gets worse and worse, and eventually, even the toughest fish will begin to suffer.

What happens in many cases is the fish respond as they do to the dry season. As their habitats evaporate, they gather in smaller and smaller, more and more mineral and pollution filled pools. They dial down their activity levels, and become more and more dormant as they wait for the rains. They can survive a long time like that. When I was a kid, no one did water changes and fish didn't directly die, though their lives were way shorter.

If you decide to do more than top up, you will have very loaded water. You will have to change it slowly, maybe 10% at a time, or the rapid change will kill the fish. I've made that mistake and learned from it.

 

[StripySnailGirl04]

Hmmm, your water shouldnt evaporate to such a massive amount that you need to add water. Probably almost harmless to do but does your tank have a lid? How much has your water evaporated?

Wait, I know what you mean now. Sorry.

 

[AbbeysDad]

Glad you asked...
There are some that swear by little or no water changes...but they are few and far between. I'll admit that in some rare cases, with a low bio-load, lots of plants, especially fast growing floating plants, and advanced bio-filtration, water changes can be reduced, if not eliminated. But these are exceptions rather than the rule. And most hobbyists have a sufficient, if not excessive bio-load and not enough plants to keep water quality high. I generally recommend 50% weekly water changes and on my well populated grow out tanks, I do 50% twice a week.
Remember, "There's no such thing as too much clean, fresh water!". I offer the deep dive into Filtration and Water Quality.

Footnote: Like all creatures big and small, fish want to live. They will survive if/when water quality is poor. But make no mistake, surviving is not necessarily thriving. Think of us humans living in heavy (smog) air pollution vs. clean, fresh air!!! Anything and everything gets into fish through osmosis. Clean, fresh water is the very best medicine.