Tank maintenance & water change frequency

AbbeysDad

DKRST,

In round numbers, I think we'd need to do bi-weekly 35~% water changes to approximately equal the 50% weekly change in terms of 'crud removal/dilution'. (note: that's just off the top as I didn't bother to make my head hurt with relational equations as I'm not sure we really need to be so precise)

I also think the water change requirements are based on the specifics of the tank. The bio-load, living plants and to a degree filtration - even a bubble wand can make a difference in releasing unwanted gases.
Maintaining water quality is multi-dimensional and we can only speak in general terms.
(e.g. the over stocked tank might be maintained with more frequent/larger water changes, while the under stocked tank can be maintained with less). To say that all tanks would be fine with x% weekly or y% bi-weekly water changes would not necessarily best serve all circumstances.

Byron

AbbeysDad, "crud' is the term coined by David Boruchowitz in a two-part article on this very issue of water changes. He uses "crud" to cover all the stuff we can't detect but fish produce, and which can only be removed by changing water.

And DKRST, that article did what you are propsing exactly; David worked out the mathematics and science on the effects of daily versus weekly water changes, and using amounts from 10% to 70%. It is in the November and December 2009 issues of Tropical Fish Hobbyist if you want to see it. If you have a subscription to TFH you can see this online (their magazine is now online as well as in paper, back to about 2006 I think). But I happened to have scanned these for someone, so I can send them to you if you PM me with your personal email [can't have attachments to PM's on the forum, so has to be your own email].

Byron.

zof

While I agree that if you let nitrates get to 30 or 40 ppm to signal a water change you have already failed, its important we know how much and how fast waste is building up in the aquarium. While 50-70% water change might be a good catch all for a water change many times with a light stocking in the aquarium a 20-30% water change will accomplish the same as the 50% in a fully stocked tank. Sure the fish wouldn't mind the extra fresh water but do we really need to waste that much extra water for lighter stocking on the tank (unless of course you drain the water into a garden in which switching the extra water you would put in the garden with the tank water would make perfect sense). The testing we do is a tool to help gauge these things and should only be used to help estimate what is right for your aquarium but is not a trigger for those things.

DKRST

The response title on this post says it all, and it's kind of a "duh" thing. Wow - cleaner water is better for our fish, who would have ever thought that

Ok Byron, I am thoroughly convinced! An excellent article with sound logic and the math to back up all the assertions. The math is simple and doesn't lie. I'm going to do much larger water changes than I currently perform, but that also allows me to do them a little less frequently and keep a lower average level of pollutants in the tank. I'll probably stick with two changes of around 50-60% a week in my smaller non-planted tanks and go with one large, 60-70%, in my planted 55. That will allow me to use a modified EI nutrient dosing in my 55 much more safely (won't have to worry about build up of nutrients).

Thanks again Byron, I learn more from your daily posts than I'd learn in 5 years on my own.

Byron

I think we're really talking of two different things. First, there is the stuff that causes nitrates to rise (if unchecked), namely the visible "waste" from fish that become organics and should be handled by the bacteria and live plants. Second, there is the "crud" that you simply cannot measure, but we know it is there because there are fish.

Both are in proportion to the fish load, true, but they are not necessarily related. As an example, in my tanks with all my plants, the "waste" is easily being handled. I see nitrates < 5ppm and have for years. It doesn't matter how many fish, relatively speaking; the nitrates are minimal because of the plants, snails and bacteria. So if I took nitrates as an indicator of a water change, I would never do one, and my weekly water changes are really not impacting "waste" at all because I never remove it from the substrate. Of course, if I never did a water change, the nitrates might rise. But with all my plants, I'm not sure this might not take a while, by which time the "crud" issue would be out of control. And given the number of fish I have in my tanks, the "crud" is the real issue and it is completely undetectable, or at least until it is too late when the fish's response would alert me if I let it go that far.

The fact that my fish respond so enthusiastically to a water change when all the test parameters remain excellent is proof of this as far as I'm concerned. The invisible and undetectable "crud" is getting removed by 50% every week, and this has a significant impact on fish health.

It is true that with few fish the "crud" would be less too. Those planted tank folks advocating no water changes are quick to point out that it works if the fish load is "moderate" and the plants are heavy. I recall reading one author who said the "no water change" works fine provided the fish are "balanced" and the example he used was 6-7 Neon Tetra in a 55g tank. The plants could handle everything at this level of balance. Most of us keep more than half a dozen small fish in a 55g tank.

Byron.

HMlairy

I do a bi-weekly 30% water change/gravel vacuum. That keeps the nitrates away generally