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Water changes and how they effect an established tank.


William_
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My wife and I have recently dove head first into this hobby and we love it. I am a bit confused about the water changes on a cycled tank. We have a 29 gallon that has been running about 2 weeks. I tested the levels along the way and when I saw the ammonia make its way into being nitrates at a concentration of 40ppm I did a 50% water change. tested again and they were just under 20ppm maybe around 10ppm. After a few days I did another water change and the levels were around 5-10ppm (I have the API freshwater master test kit).

My question is : We got some guppies to put in the tank and of course then came fry. Just before this happened we had a huge nitrite spike of 5ppm. I did the necessary water changes to get that back to normal and everything has been fine since. The real question, is doing to many water changes going to hurt the fish? Even if both types of bacteria are present and doing their job, will removing and replacing to much water hurt the cycle and is it dangerous for the fish, especially the fry?

 

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As a rule water changes aren't harmful as long as the water going in is healthy and stable. The most expensive fish in the world (Show quality Japanese Koi) typically have constant water changes in their mud ponds as the water in the ponds is constantly being replaced with fresh water coming down nearby mountain streams. Discus breeders often do 90% water changes on a daily basis. Some hobbyists have a drip system set up where fresh water is constantly dripped into their tanks and excess water is removed through an overflow. If you're willing to change enough water frequently enough you don't even have to cycle a tank as the levels will stay low enough. Most people aren't that crazy though. 

Water changes can be harmful if the new water is vastly different, warmer/colder, vastly different pH, etc., but by and large a water change isn't dangerous and won't harm a fish. The most expensive fish in the world typically get large water changes on a daily basis. The breeders and keepers wouldn't do that if it was dangerous.

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That many water changes will hurt your back before they hurt the fish. Don't chase the numbers.  As long as your readings remain in the safe range, the fish will adapt.

I would suggest a 10-20% water change once or twice a week and see where the numbers settle.  If you haven't done it yet, some plants like Hornwort, guppy grass or other fast growing floaters will help use up some of the excess nitrates.

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Thank you for the info guys. My worry is removing the water too much will also remove the food source for the Nitrosomonas and Nitrobacter Bacteriums. Causing a massive die-out in the filter and on the substrate spiking the ammonia and killing all my fish before the Nitrosomonas bacterium can come back to reassert the cycle. Any thoughts?

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5 minutes ago, William_ said:

Thank you for the info guys. My worry is removing the water too much will also remove the food source for the Nitrosomonas and Nitrobacter Bacteriums. Causing a massive die-out in the filter and on the substrate spiking the ammonia and killing all my fish before the Nitrosomonas bacterium can come back to reassert the cycle. Any thoughts?

Nah, this won't be an issue. Your fish are constantly producing ammonia so there will always be some in the tank to be removed by the bacteria. 

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I test my tanks constantly. They're on a rotational schedule so I always know the levels. The ammonia and nitrite are almost always 0ppm but the nitrate holds a steady 10-20ppm range which I remove with water changes of course. I don't have a lot of plants, mostly moss, so the nitrates don't really have a place to go. Are the Nitrosomonas and Nitrobacter really that efficient in converting ammonia into nitrite and then into nitrate respectively, or perhaps I don't have such a large load that the levels would fluctuate as I've seen in examples by other people?

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And on another topic; Is there any books or website dedicated to the aquatic nitrogen cycle? I've read books on the nitrogen cycle for Agricultural science but nothing purely on the aquatic nitrogen cycle itself and how it relates to the health of both the fish and plants in my aquariums.

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8 minutes ago, William_ said:

I test my tanks constantly. They're on a rotational schedule so I always know the levels. The ammonia and nitrite are almost always 0ppm but the nitrate holds a steady 10-20ppm range which I remove with water changes of course. I don't have a lot of plants, mostly moss, so the nitrates don't really have a place to go. Are the Nitrosomonas and Nitrobacter really that efficient in converting ammonia into nitrite and then into nitrate respectively, or perhaps I don't have such a large load that the levels would fluctuate as I've seen in examples by other people?

Unless the tank is way overstocked, they are being way overfed, or something like a dead fish is rotting in the tank, ammonia and nitrite levels should be 0 or very close to 0 at all times. Now, if you added a large number of fish to an established tank that could cause a spike, because there would not be enough bacteria to support the added bio load, but it would not take long for it to catch up.

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31 minutes ago, William_ said:

Are the Nitrosomonas and Nitrobacter really that efficient in converting ammonia into nitrite and then into nitrate respectively, or perhaps I don't have such a large load that the levels would fluctuate as I've seen in examples by other people?

Yes! They really are that efficient once everything’s established. In my experience the ammonia-nitrite conversion seems to happen a bit slower than the nitrite-nitrate conversion, but I haven’t done any tests to back that up.

@Daniel’s collected some awesome data on cycling and made graphs and everything. He can probably point you to that post.

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6 hours ago, Hobbit said:

Yes! They really are that efficient once everything’s established. In my experience the ammonia-nitrite conversion seems to happen a bit slower than the nitrite-nitrate conversion, but I haven’t done any tests to back that up.

@Daniel’s collected some awesome data on cycling and made graphs and everything. He can probably point you to that post.

As @Hobbit the ammonia-nitrite conversion seems to happen a bit slower than the nitrite-nitrate.

Here are some graphs from the dirted tank project showing ammonia rising first, then nitrite, finishing up with nitrate:

image.png.165c29a5a55ceb2e0842b47b10c63f

But not all cycles are the same. This tank had soil in it higher ammonia on day 1, but once the ammonia dropped it became a more classic progression (the nitrite and ammonia dropped a couple of days after this graph):

image.png.1b6f9eefd56ebedbb1a701d8b4d9c2

And probably the most important thing to remember with the above graphs is that all of these aquariums had healthy happy fish in them the entire time the tanks were cycling.

Here a photo of the 'Dirted' tank above from November 6 (a high ammonia day).

709073145_FullShotNovember62020.jpg.d55f

Nothing about high ammonia or nitrites gave any visible signs of distress to the angelfish and guppies in these tanks. People stress over this way too much sometimes.

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