Can you do too much water changing?


After reading lots here and members comments that you all seem to want some nitrates - I'm wondering if any harm can come from too much water changing.

Our freshwater systems filters are outside and have overflow so extra water just drains to the ground- that allows us to have easy water changes with a timer valve that just adds water daily. Currently we do around 20% change daily but could do more or less.

My work has been with frogs and there is no such thing as too much water change - we have some frog and tadpole systems with 10% change every 2 hours. So I assumed that would apply to fish too.

Am I wrong? Could too many water changes be bad?


As long as it's not something like 100% every hour I wouldn't suspect a problem If the source water is the same as the tank. Maybe with caridina shrimp you could get into some trouble (even then maybe not), but I'm pretty sure frogs are hardy right?


It sounds like you have the perfect system. I wouldn't change a thing about it. I don't believe there is such a thing as too much fresh water so no, I don't think you can change too much water. A tank doesn't need nitrates although some nitrates are good if it is a planted tank. It is just that most cycled tank do. Seeing nitrates if one has no nitrates in their source water is a good indicator of a completed cycle.
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Thanks- I'm sure our fish system is far from perfect but I'm glad our water change system is ok for fish as well as frogs- we have limited experience with fish so are grateful for any advice - Thanks for your help.


Hi Alejandro
Nitrates are bacteria poop not the bacteria themselves.
Asking people if they have nitrates is one of the few ways to ask if the tank has a working nitrogen cycle when it’s not clear the person has a full understanding of what cycle means.

There is no such thing as to many water changes.

A river or stream is an example of fish and shrimp living with several thousand percent water changes daily.

From a Financial point of view yes it’s a waste of money to change more water than is necessary to keep the water fresh.


I limit my changes based on buildup vs depletion but it's not for (only) the health of the fish, it's to stay on one side or the other of a nitrate/phosphate relationship. If the total parameters are still within the fishes threshold, it's the best I can do.

With my water source, a 24/7 water drip would be perfectly safe and likely the healthiest for my fish stock, assuming they were all soft water fish. But it would be detrimental to my planting, unless I also injected fertilizers and water hardeners. I use planting to keep the fish stress free, improve asthetic (selfish humans) and stay within safe parameters for the fish naturally without having to add nitrogen or phosphorus. By limiting my changes I am able to mineralize my overly soft water and give the fish a more stable pH and source of calcium, potassium, magnesium, iron etc. Otherwise I'm constantly so soft harlequin rasbora breed non-stop and guppy grow crooked, snails turn white and chalky.

When I'm breeding endler/guppies rapidly, the many smaller grow out tanks get a pretty steady daily water change like your tanks, but those tanks are bare, ugly utilities that serve a simple purpose. They are also easy to mineralize due to their smaller sizes. The tanks I hold back the changes on are a whole wall worth of my family/sitting room, theycreate a peaceful area to read, draw and watch nature, minimally planted, not so much. The grow out tanks are so ugly the couple months at a time I run them my wife asks me daily when I'm going to put them away.

The only time I would think your fish might suffer from constant drip waterchanges would be if your water lacks the minerals required to grow healthy fry, or if it is over treated like some city water can be. Basically if you have to buffer, it would make it more complicated and excessively expensive.
  • Thread Starter


Thanks all

Our water supply is soft (only 40ppm) but ok I think - certainly perfect for the frogs which is my main work. Fish are my son's hobby but he has been able to tap into my frog systems.

We run all our animal water from the city mains through carbon and sediment filters which is then sprayed into a large holding tank. This system then pumps out to the frog rooms and Alejandro gets to use it for his fish. It's all automated and we use thousands of litres daily in frogs so Alejandro borrowing 100l per day for his freshwater fish is no issue. (His marine tanks are the real water chage nightmare).

We are grateful for the advice - and hadn't thought about minerals but also haven't seen development issues - he has shrimp breeding so I guess they would suffer if low minerals was an issue.

In frogs they are very good at bioaccumulation of minerals so depleat water very quickly - high change volumes even if the water is soft compensates for this. I assumed (correctly?) That fish would be similar - but I guess their uptake mechanisms are different.

Either way I guess we'll learn and I hope continue to share here - some frog techniques may be transferable to fish and perhaps that can help others with ideas.

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