It is hard to find unpolluted soil. There are always pesticide, chemical fertilizers, and herbicides in most soil you can find. They can be harmful or even deadly to the fish.
Partial water change every 3~4 months is a little extreme. The water change we do is not just for removing the nitrate, but also to restore the water buff, minerals, etc. There are also other organic waste we can't see beside nitrate. Unless the aquarium is heavily planted with very few fish, the need for water change is definitely more frequently than once every 3~4 months.
It's really not that hard to find natural unpolluted/unfertilized soil without pesticides. You have to pay attention, but it is out there, more and more every day. I mean, if you are going to look at Wal-Mart & Home depot, you might have problems, but with a little effort, it is really no problem.
(02-18-2017, 02:05 PM)GreenAmy Wrote: @ Thor,
I definitely recommend reading the book if anyone is thinking about trying soil. One is taking risks, and the author speaks to many of them. Her tanks are heavily planted and sparsely populated with with fish. I will probably not have my tank as heavily planted as the author and plan to do weekly 20% changes because they make more since to me than doing a larger exchange less frequently. Plus I don't want to restrict my fish population as much. Like I said you can't just run out to Walmart and throw it together with no thought. I just found it interesting that she is able to do it and have tanks that have plants and fish that have been thriving for years. She is a long time hobbiest and microbiologist.
I have never actually tried the Walstad method, nor read the book. But the idea is sound, if you do it properly. I have read many posts and articles by her disciples over the past few months. It can work.
Water changes primarily do two things.
1. Remove/dilute toxins. Primarily nitrates and phosphorus. Which are two of the three most important nutrients plants need. I consider my tank moderately planted, and I am already at the point that I have bought both phosphorus and nitrogen to add to the tank (more the P then the N). The Walstad method relies on this. Without enough plants it doesn't work. With enough plants, they will filter nearly all the toxins from the water. I absolutely can't keep a detectable trace of P in my tank for more than 3 days, using two different brands of tests.
2. Replenishing trace minerals, potassium, & carbonates. Again, all easily replenished without water changes. There are plenty of people with soft water tanks that only use RO water which ash no minerals or carbonates, so if this was a true reason you needed water changes, they'd all be screwed. They add back all the minerals they want &/or need. You can do the same to a runing tank. You need test kits to do this properly IMHO. You need to know what is in your tank, how fast you are going through it, and what is in the water you are using to replenish it. Plus the knowledge of what it is you actually need.
Short answer, if you pay attention to what you are doing, and learn what you need to do, you can get a much healthier tank doing this than just doing ritual 20% water changes on a schedule. Of course, if you aren't on top of what's going on, you can make it much worse.
