Frequency and amount of water changes? Hypothetical scenario

Alright, so I do not own any fish currently, but I'm trying to learn(and wow, is there a lot to learn). I've seen LOTS of different information about water changes(how frequent to do the, and how much water to change).
Imagine an aquarium(which is probably similar to what I would have if/when I have fish). It would most likely be a 10 gallon(maybe 5), with just one betta in it. It probably would not have a filter(I think I read somewhere that filters aren't good for bettas?).
So in this hypothetical aquarium(which might not be a good setup in the first place, but I don't know), how often and what percentage of water changes would I do?
I read that the more frequent the changes and the larger they are, the healthier the fish will be, but I've also read that 100% changes are bad for fish. Is there a magic percentage for unfiltered 10 gallon tanks?

Sorry if this is a bit confusing, I'm just drowning a little in all the fish care information.

Bettas can have filters, in fact it is better to have a filter with a betta as it means less water changes. What needs to be avoided is filters with strong water flow. Those sponge filters powered by an air pump are ideal for bettas.

With a filter, I would do 50% water changes every week. That's what I did when I had a betta. Without a filter, they need to be more often, possibly every day depending on the ammonia and nitrite readings in the tank. Any reading above zero means doing a water change.
Live plants also help as they take up ammonia from the fish but they don't turn it into nitrite. This doesn't mean that with plants but no filter water changes don't need to be done as fish excrete lots of other things besides ammonia which still need to be removed.

We have a care sheet on this forum, written by an old member who was an expert in bettas of all species

CuriousFins said:

Alright, so I do not own any fish currently, but I'm trying to learn(and wow, is there a lot to learn). I've seen LOTS of different information about water changes(how frequent to do the, and how much water to change).
Imagine an aquarium(which is probably similar to what I would have if/when I have fish). It would most likely be a 10 gallon(maybe 5), with just one betta in it. It probably would not have a filter(I think I read somewhere that filters aren't good for bettas?).
So in this hypothetical aquarium(which might not be a good setup in the first place, but I don't know), how often and what percentage of water changes would I do?
I read that the more frequent the changes and the larger they are, the healthier the fish will be, but I've also read that 100% changes are bad for fish. Is there a magic percentage for unfiltered 10 gallon tanks?

Sorry if this is a bit confusing, I'm just drowning a little in all the fish care information.

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Water changes will be easy on a 10 G tank. I would do 75% weekly with a filtered tank. My betta is in a 10 G with a small foam filter, very inexpensive. Never had a fish tank without a filter, so can’t advise you there. Whatever you do, get an API master test kit & monitor ammonia, nitrates etc.

Yep as above, you definitely want to use a filter. Even a small air power sponge filter would do the job and they are actually pretty easy and cheap to make (search for DIY sponge filter). An undergravel filter works great in a betta tank as well and can also be DIY'ed cheaply and easily. Plants are also highly recommended.

With a filter I generally do 20-50% water changes once a week.

Here’s my betta boy. The small sponge filter cost under $5. You’ll need the air pump too.

The chemistry of the water changes over time due to plant removing nutrients from the water, fish waist, and evaporation. So water changes are done to keep the chemistry of the water stable. If water changes are not done the water will get hard over time, and it may eventually become toxic to the fish. How much water to change and how often is necessary depends on a lot of factors and it it is difficult to predict.

When a water change is done it is best to use water with with the same temperature and similar chemistry (GH/ KH/ PH). If the chemistry is very different and sufficient water is change. the fish might get shocked and could die. I personally do a water change of 50% once a week. I know before hand what the KH/ GH, and PH are (typically very close). Doing a 50% change insures you have 50% old water and 50% new water so if I don't notice a parameter difference the change in the tank will only be 50%. For larger water change any chemistry shift will be larger. Smaller water change will have a smaller shift in chemistry. However smaller water changes may not be able to keep up with the gradual chemistry change that occurs in the water. So after several months the water chemistry will still shift.

You are generally correct. But I have removed 75% twice on some days due to a nitrate spike & weekly for a large cichlid tank. The tap water where I live is stable.

JennySolano said:

You are generally correct. But I have removed 75% twice on some days due to a nitrate spike & weekly for a large cichlid tank. The tap water where I live is stable.

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Nitrate occurs within the biological system, and while water changes are often said to be aimed at nitrate, there are other factors as important and even more important, all aimed at keeping nitrates as low as possible and not fluctuating that much. Nitrate entering via the source (tap) water is obviously another problem, but staying solely with the aquarium biological system...stocking at or under the limit the tank can handle, not overfeeding, keeping the filter clean (rinse out all the organics every week if that is necessary), vacuuming the substrate in open areas, having plants that are fast growers (floating ideal), and of course, water changes.

This is not meant to be critical, but there should never be nitrate spikes. If one occurs, then there is a problem with the biological system. The issues mentioned above.

I don’t think you want to hear how I won the nitrate battle

Thanks for all your answers! Would it be different in a 5 gallon(and would that be big enough)?

That may depend in part on what’s in the 5 G. Are you planning on a 5 G? Sorry, I’m forgetting now. Are you the person getting a betta?

Good tank maintenance is the same across the spectrum. I won’t be doing much different in my proposed 125 G than I do with the 10 G betta tank, just on a larger scale, like 2 huge filters. Big & ugly!

JennySolano said:

That may depend in part on what’s in the 5 G. Are you planning on a 5 G? Sorry, I’m forgetting now. Are you the person getting a betta?

Good tank maintenance is the same across the spectrum. I won’t be doing much different in my proposed 125 G than I do with the 10 G betta tank, just on a larger scale, like 2 huge filters. Big & ugly!

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I'm not so much planning as wanting to plan to get a betta. So I'm not sure if I would house it in a 10 or 5 G. I was asking if the amount of water you changed weekly would change if it was a smaller tank.

I see. Probably more people do <50% than my higher percentages. i had to come up with an easy water transfer system for my 90 G, so once it’s set up, no additional work to move more. I do skip some weeks if the params are good.

I have a betta in a 10 G. He’s beautiful, but I have a preference for fish that can be kept in groups.

I have only ever done weekly 25% water changes on my tanks.

CuriousFins said:

I'm not so much planning as wanting to plan to get a betta. So I'm not sure if I would house it in a 10 or 5 G. I was asking if the amount of water you changed weekly would change if it was a smaller tank.

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Generally in smaller tanks you want to aim for the higher end (i.e. 50% weekly). There is less water volume which means less dilution of things like nitrate. Also its easier to do a 50% change in a 5G than it is in 100G.