I think of it in terms of a fish's natural environment, which for the fish I keep means streams and rivers. They are constantly replenished by rainfall and constantly moving, which means the water is constantly changing. As Byron points out, there's a chance a fish is only in the same "water" for les than a second.
I've been free-diving in areas where I have caught rainbow fish. Practically speaking, the amount of water per fish is much much more than in a home aquarium. Let's say I took an "average" 4 foot aquarium and scooped out that quantity of water from a local stream, I'd be lucky to have three fish in it (pretending the fish wouldn't escape as soon as they saw me coming), whereas I'm quite happy to have 8 or 10 rainbows in the same amount of water at home. I feel a 40% water change weekly isn't even scratching the surface of what would happen in a stream, but it seems to keep my fish healthy.
If you change you shower analogy to a bath, how many days in a row would you bathe in the same bath water before changing it?
By the way, I commented on another thread recently that I don't bother checking my nitrates any more due to the fact I have a fair quantity of plants and I watch my fish's behaviour. I got curious, so before I did my last water change, I checked and I have 10ppm nitrate in a tank with week-old water, and 20ppm in the tank I've been quite neglectful of and hadn't changed in a fortnight.
I've been free-diving in areas where I have caught rainbow fish. Practically speaking, the amount of water per fish is much much more than in a home aquarium. Let's say I took an "average" 4 foot aquarium and scooped out that quantity of water from a local stream, I'd be lucky to have three fish in it (pretending the fish wouldn't escape as soon as they saw me coming), whereas I'm quite happy to have 8 or 10 rainbows in the same amount of water at home. I feel a 40% water change weekly isn't even scratching the surface of what would happen in a stream, but it seems to keep my fish healthy.
If you change you shower analogy to a bath, how many days in a row would you bathe in the same bath water before changing it?
By the way, I commented on another thread recently that I don't bother checking my nitrates any more due to the fact I have a fair quantity of plants and I watch my fish's behaviour. I got curious, so before I did my last water change, I checked and I have 10ppm nitrate in a tank with week-old water, and 20ppm in the tank I've been quite neglectful of and hadn't changed in a fortnight.
