Advice on water change intervals

[TokyoBetta]

helllo

I have a 19.845L tank, that's I think 5 gallons.

It's heated at 28*C/82.4*F

I have two live plants in there in good condition.
The tank is unfiltered so I do one full water change and cleaning once per week without fail.

Each time I do the change I use water prep tablets then one scoop of mineral salts.

I'd have to guess my fish is pretty happy but I notice that he doesn't like to make his bubble nest until around the time I'm getting ready to change the water.

At that time sometimes the gravel has minute amounts of algae but generally the tank is still clean.

Can he go maybe 2 weeks at a time? When he starts to make the nest is the water the right perhaps the kind of natural dirtyness he'd live in in nature? Or even though he's happily making his nest is it possible the water is becoming dangerously unlivable?

I'm just a bit of a 'naturalist' and figure if he's happy making a nest why change the water?
But then that doesn't mean you want to wait till he's suffering to change the water either, so if 1 week is still the most optimal and safest route that's fine.

I read something about partial water changes but I think that was for filtered tanks?

Thanks for any advice

[Vincent]

I'd go 4 days TOPS with a 100% water changer in a unfiltered 5g, unless you have live plants and then i'd let it go another day or 2

[Oldfishlady]

What kind of plants do you have in the tank, by adding more live plants you can go longer between water changes-depending on the type of plants that is....fast growing stem plants and floating plants are great at maintaining water quality instead of filters-the plant is the filter...but you need more than a couple of plants.

[Vincent]

Do you have that clear sticky protein film on the top of your unfiltered tanks?

[TokyoBetta]

By the time I change the water there is a very slight sticky film on the top.

Oldfishlady, I'm not sure what kind I have.. but could you perhaps recommend a few that are good for water quality? I'll go out and buy them! I like having the plants and so does Sam, so a couple more won't hurt.

[Oldfishlady]

Good floating plants-water lettuce, hornwort. wisteria (floating and planted)
Stem plants-hygrophilia's, ludwigia, rotala, naja grass, are a few-but any stem type plants are good fast growers-they are usually sold in bunches

The scum on top of the water is usually organic and harmless...... caused by fish, food, decaying plants, oils in the air, pollution, oils on your hands etc......you notice it more in non-filtered tanks or tank that have limited flow because the filter keeps it broke up-easy to remove with a paper towel lightly laid over the surface.