A charcoal filter is not really enough of a filter to keep fish healthy. If the tank is small (and it is), you could treat it more like a large aquarium. Look into purchasing a Fluval canister filter. They are very easy to install and you can include charcoal along with bio-media for proper filtration. Charcoal will remove a certain amount of toxins, but fish produce ammonia and you need voi-filtration to handle that. You don't need to do a huge water change now (that would shock them unnecessarly), but really should start doing 10% changes a week. The nice thing about those pondmaster pumps is you can hook a garden hose right up to them. Simply get a length of hose and run it out into the yard.

There is a bio filter too, in combination with the charcoal.

So the possibility of buildup of minerals/ chemicals is a non issue?

It seems to me that as time goes on these would become more concentrated even with the periodic water changes (lime + other minerals from water, plus all the stuff that gets added = whatever that stuff is in dechlorinator, and I think I added salt at one point) But maybe its nothing to worry about.

If you do 10% water changes per week,it is a non issue. If you never change the water and only top off what evaporates, it can be a very big issue.

Yes, partial water changes take out the accumulation of heavy metals and salts.

I think it would be very stressful to remove most of the water and add new over several days. That will probably kill the fish!

I've had an aquarium set up for years and have never done anything that drastic. Partial water changes are the key to keeping an aquarium healthy. Anything drastic is like starting over. The aquarium itself has a healthy beneficial bacteria microsystem in it. I clean the gravel at the same time I take about 1/4 of the water out and fill it back up.

Hi
Have maintained one pond since 1982 with only partial water changes though it's exposed to rain so there would be more total water changes. Still seems to be running fine though raccooons ate the fish lol
What I've found over the years is the build up of debris will eventually require a startover in an aquarium or pond.
My above ground pool has been invaded by marshmallow and the only way to remove it is cut it out. So i'll be redoing it come spring. several of the plants have become so dense that there is no swimming room.
I recently hooked up a 1000 gallon pond to a 150 gallon aquarium with an automatic water changer using rainwater from the roof. I'm rather surprised at the amounts of water being changed in even a 2 inch rain. Maybe too much of a good thing?? lol
I would stick with the partial water changes in your case unless you have a lot of buildup.
gary

I've kept aquariums for decades and I just use distilled water for topping up tanks. It doesn't add any minerals like tap water would. I'm not a huge believer in water changes because I keep a very uncrowded tank -- I rarely (maybe 2-3 times a year) replace 10-20% of the water (mostly because so many people say I should rather than because I see any real need for it) and my fish and plants are always strong and healthy. I use a standard hang-on-the-back filter with the usual pad/sack containing charcoal, but I've found that the type of charcoal makes all the difference in the world. I saw a dramatic change in my water's appearance when I switched to Kent Marine Reef Carbon (made for saltwater tanks, which have fantastically more critical water quality standards than freshwater tanks.) The water was clear before, I thought -- now it's like looking into a polished crystal. This kind of carbon is pricey compared to ordinary "activated carbon" but it's well worth the extra $$, I think. The fish were happy before, but now I'm happy too!

Well OK I think I'll chill out about the water but...

I still think the minerals would tend to become more concentrated over time even with partial water changes. BECAUSE... evaporation is still occurring, whether the water changed or not. But maybe its just not significant amt. so why worry about it.

Secondly, to comment on an above post. Changing a lot of water won't kill fish any more than introducing them to a new pond or tank would. Once my tank lost most of the water due to a freak siphoning accident and the fish survived quite well. The new water was added VERY gradually, similar to how you introduce fish to a new pond by graadually mixing the old water with new.

But there again why do it if you don't have to is the conclusion Ive come to.

Plants remove nutrients and minerals, but they only take what they can use. It is possible that some minerals, like copper, are introduced in fertilizers, food, or water treatments, but are not removed by plants at the same rate as they are introduced. Eventually these could build up to the point of toxicity. That being said, I think it is obvious that some water changing must happen, but I don't think the water changes need to be excessive. I do a 20% change two or three times a year and I get some natural overflowing in the rainy season that probably changes at least that amount of water.

I suspect that any pond with plants could go a year or more with no changes at all before trouble would set in.

I wouldn't do a 100% water change without a really good reason, like replacing the liner, or something like that.

Have you tested your waters chemistry? It will tell you alot about whats happening.