Generally speaking, you're not supposed to be changing that much out each week. Normally it's less than 50%, but if it works, I guess it's fine. But, to answer your question, I'm pretty sure the answer is yes, if the aquarium is heavily planted and with water changes that large. After all, nitrates are the finishing product of the nitrogen cycle. Hope this helps.
We have sufficient scientific evidence these days to be able to answer the question of water changes better than we could with as much degree of certainty several years ago. I'd like to offer some ideas to think about.
Pollution accumulates in an aquarium with fish on a regular and consistent basis. No filter can adequately deal with this pollution, except live plants but this is quite limited considering how most of us stock our tanks. Removing the "old" water and replacing with fresh is still the only way to deal with this issue. So that brings up the question, why do we need to do this in the first place?
Fish in their habitats do not live in the same water for more than a second, the time it takes to respirate once. The next "breath" they take will be "fresh" water. This is next to impossible to achieve in an aquarium, unless you have a flow-through system where water is flowing out at one end and being discarded (like, into the drain) and fresh tap water is flowing in at the other end continually. Even public aquaria can't usually have this, so we use water changes to get as close as we can. Because this exchange of water is crucial for the health of the fish.
The "pollution" that accumulates includes ammonia, though bacteria and live plants should be able to handle this. Then we have urine--a small tetra can void up to 1/3 of its body weight in urine every day; this urine is simply "stale" water, which is the tank water entering the fish by osmosis through every cell, being treated by the kidneys, and then expelled. Then there are chemicals like pheromones and allomones released by all fish. No filter can handle these (urine and chemicals) adequately if at all. Then there is the remnant of the solid waste the bacteria in the substrate and filter do deal with initially, but what is left behind dissolved in the water can only be removed via a water change. And there are trace minerals that need replacing.
Leave a glass of plain water to sit out for a few days. Then drink it, and drink water from a freshly drawn glass. You will see quite a difference. And there are no fish in this water, yet it is still being acted upon.
That brings us to the volume. This partly depends upon the fish load (number, sizes, and compatibility factors all factor in), water volume (tank size), live plants and filtration. The greater the load on the biological system, the more water needs to be changed. But rather than think of the minimum we should change, to avoid emergencies, it is better to consider how much we can change to keep the fish healthier. Prevention rather than treatment is always better for the fish, and easier for the aquarist.
When you remove a certain amount of water, you are only removing that percentage of "pollution." As a simple example, if we have a 10 gallon tank and the fish load adds a specific percentage of pollution--we'll give it a number so it is easy to fathom, say 100 ppm, removing 25% of the water is only removing 25% of the total 100 ppm pollution; the rest (75 ppm) remains. During the week, the fish add the full weekly amount of pollution, another 100 ppm, so at the next water change we now have 175 ppm pollution. Removing 25% of the water will this time remove 25% of 175 ppm, leaving 131 ppm of pollution. And the next week it increases again, and so on. So no matter what, the more water you change, the better for the fish.
Changing 10% every day for a week is not even close to the benefit of changing 70% once a week, due to the continujal increase explained above. So the larger the volume, the fewer times you need to do it. And even doing it more often, at smaller amounts, is not going to have as much benefit as doing one larger volume change each week.
Some discus breeders do two or three 95% water changes every single day. They can stock the "grow-out" fry tanks with more fry this way, and the fry grow faster and are healthier. The benefits of water changes really cannot be overstated.
I do 60% or maybe a bit more on each of my 8 tanks, every week without fail. This is the best way to ensure stable parameters, good water quality, and healthy fish.
Byron.
