I'm in a hurry, but in a nutshell if you have a big tank that is densely planted and quite a bit understocked with fish, could you get away with less water changes? Maybe test the water weekly and do a change once the nitrates start getting up to a certain level?
You could, but you have to keep in mind that there are other pollutants in the water besides just the nitrates. Even if the nitrates stay within range with fewer water changes, you could still have what they call "old tank syndrome" which is basically where these othertoxins build up in your tank and your ph gradually drops until it just crashes and could kill all of your fish.
Oh ok that's good to know...
But, do you think it would be ok to do changes only every other week, or maybe only very small changes? It would take a while to explain exactly why I'm asking this, but let's say the tank is 30-50 gallons, well-planted, and only had a shoal of Neons, say 10 of them for 30 gallons, a few more for 50. I just figure in such an understocked tank the toxins would take a lot longer to build up, but be honest if you don't think less than weekly water changes no matter what is a good idea.
Yes in a large, well planted tank, under stocked tank you could do water changes less often. Say every other week instead of weekly. But I wouldn't want to go longer than that, and not all the time. As well as pollutants that need removing there are things that need to be replaced with water changes.
Omorrokh, I know you're in a hurry now. But if you ever have the time, please read "Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise for the Home Aquarist" by Diana L. Walstad. I think the author talks about something precisely that you have in mind. You won't regret having read this book if you are seriously thinking about having larger heavily planted tank, and without CO2 injections. I think I will use this book to set up my future heavily planted tank. The book is not expensive either - a new one on Amazon.com is around $20; if you'd like a used one, I'm sure you could find it much cheaper, also on Amazon.com.
I agree with Carol and Gunnie that there may be chemicals other than nitrate accumulating in the water over time without frequent water changes. However, thanks to the book above, I also have a little different opinion now. The book explains how having a very heavily planted tank actually eliminates the need for frequent water changes. Provided that you have appropriate rooting medium (soil at best) and A LOT of plants, you may not need so many water changes at all. This is because plants "filter" the water in a way. Plants actually do consume not only ammonia and nitrite (and nitrate to a lesser degree) but also a lot of toxic chemicals and heavy metals that accumulate in water over time. Plants also use fish wastes and uneaten fish food! They also keep your pH stable. So if you have a very heavily planted tank, with good lighting, the plants will remove all toxic chemicals from the water and thus eliminate the need for frequent water changes. Also, if you do too many water changes in a heavily planted tank, you may be removing nutrients from the water that are plants' food. Such a tank may create an ideal self-sufficient aquatic environment. This is not to say that you wouldn't have to do any water changes, but you would definitely have less water changes. Well ... just read the book, and you'll see what I mean
I completely agree with Isabella. Heavily planted with just a few fish would certainly allow you to drop your water changes a lot. Ive always been the type of person that likes to keep the substrate to a minimum, so now I am using plants that are potted in small tubs or attached to wood. I have 16 seperate plants in my tank like this all healthy.
I would recommend 30% of your tank every fortnight. But you have to watch how you set up. You cant allow for anerobic dead spots etc. So a book is a good idea. As I said I move mine around and totally clean the little substrate I have once a week (the beauty of one tank is the level I can maintain it).
My 55 is very heavily planted,well whatever plants the cories leave rooted. ;D I do about 15% water changes every 3 weeks and just skim over the substrate once in awhile. My tank has quite a few fish in it tho so maybe you can get away with just every 3 weeks or so with fewer fish. The only tragedy's I have are old fish dieing off. All my other tanks get 25-30 water changes weekly.
Carol, the book describes how a soil bottom is free of hassle (no need of deep gravel vac. or even stirring). Soil is the best natural medium for ANY plants on Earth. After all - plants grow from soil, lol. Once the plants get established well in the soil and their roots are spread all over the bottom, they sort of "stir" the gravel themselves by producing gases that need to get out somehow - this creates movement within the soil and thus eliminating dangerous toxic pockets. The roots of plants also consume these toxic gases should they accumulate under the soil. However, I can't remember if the author said whether it's necessary to stir that soil or not. But I think not (well, I'd have to read the book again) - which is what makes the maintenance of such a tank very easy and hassle-free. The only condition is that it is so densely planted that the bottom is completely filled with roots which will prevent toxic gases from, forming and the leaves will consume all nutrients from the water thereby eliminating all toxic chemicals and metals. Like I said - a sort of "self-sufficient" environment, IF created correctly. No need for CO2 injections either. I believe this woman because she has and had many tanks set up this way and they're all successful and all fish are healthy there. The woman herself is a scientist so she must know what she's talking about. She has done a lot of research and experiments to support her book.