Tropical Fish Keeping - Aquarium fish care and resources

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gammahermit 04-05-2009 04:21 PM

what is the reason for water changes?
what is the purpose of changing the water? Is it a preventative measure to keep nitrates, nitrites, ammonia, hardness & the PH from getting to high. If the carbon, sponge, & bacteria in the biomedia keep the level of harmful chemicals at proper levels is it still neccessary to do water changes? Are there other things I am not considering that can harm the fish?

Mikaila31 04-05-2009 04:48 PM

While the biofilter takes care of ammonia and nitrite, it produces nitrate. The only way to effectively remove nitrates is to do a water change. Though nitrates are not very harmful to fish, they can be if they are allowed to build up. Changing the water also replaces the trace minerals that that the fish need. Also fish like new water. IMO fresh water is like fresh air. You know how the air is so nice out side........ fish like new water.

Byron 04-05-2009 07:10 PM

Mikaila31 really said it very well, and I'm only going to emphasize it a bit because I'm concerned that you may be contemplating not doing partial water changes and that spells disaster in time.

Fish take in water through their cells (called osmosis) and expel it as urine after they have used it to do biological processes much the same as we do. In time, they would literally be swimming in a tank of urine. Not healthy for fish any more than for us.

As Mikaila31 said, fish need minerals and that has to come from water changes because they use up the minerals in the existing water fairly quickly. If it is a planted aquarium, the same happens with plants. The nitrates produced as a result of the nitrobacter bacteria do build up if not removed; mosat aquarist aim for nitrates around 20ppm or lower; at over 40ppm they are toxic to many fish. Plants utilize some of it through the action of the bacteria in the substrate, but if there are anaerobic bacteria in the substrate (as there usually are in varying numbers) they produce nitrogen gas and hydrogen sulphide. More toxins that need to be got rid of.

There is a small school of aquarists (I suppose there still are, I haven't come across any on this forum) that advocate it is unnecessary to do water changes in a thickly planted tank with few fish. I am skeptical of their claims, and would not want to risk it. Besides, like most of us I like to have lots of fish in my tanks, and without water changes I certainly wouldn't have them healthy for very long.

It is no surprise that fish will often spawn immediately after a significant water change. I know there are a number of reasons why this occurs, but the point is that without the water change they would not be motivated to spawn to the same degree. It's natural, and as Mikaila31 said, they like it.

Mikaila31 04-05-2009 10:10 PM

Overall I agree with the above, however I have yet to come across a fish other than discus that have issues with 40ppm of nitrate. There's been reports of some fish being fine at 100ppm, personally I would worry at this level. I run 40ppm of nitrates out of the tap and I dose nitrates on top of that. Ideally you want low nitrates, but I don't test for nitrates.....

"No water changes in a thickly planted tank that is lightly stocked". I do advocate this method, its called the El Natural method. Also a filter is optional. Though I don't run any tanks using this method(I stock heavily) it is a viable method. I'm not entirely sure how water nutrients get replenished using this method. has a whole forum section dedicated to El Natural style of fish keeping, I'm sure that question could be answered there. I'm an hour from the twin cities and in the summer people have successfully bred fish outside in large cattle troughs(100-300Gal) no heater or filter, some do water changes others rely on the rain. I'm hoping to give this method a try this summer.

MBilyeu 04-05-2009 10:44 PM

The theory of heavily planted aquariums not needing water changes is almost 100% correct. As far as the nitrogen cycle goes, yes you can have an aquarium without ever needing to do a water change. Outdoor ponds do it this way all the time. The difference though is that outdoor ponds rely on rainwater to replenish minerals, where you wont have this in an aquarium setting. However you wouldn't have to do weekly water changes because the fish don't use up minerals THAT fast. I would say to be successful in one of these "Natural" tanks, you would still need a water change every few months.

willow 04-06-2009 03:04 AM

nothing better than a breath of fresh air when closed up in a stuffy room.
my corydora catfish often spawn after a water change.
and all the other fish love them for it.yum yum.

1077 04-06-2009 05:07 AM


Originally Posted by Mikaila31 (Post 185758)
Overall I agree with the above, however I have yet to come across a fish other than discus that have issues with 40ppm of nitrate. There's been reports of some fish being fine at 100ppm, personally I would worry at this level. .

Besides Discus, Threadfin Rainbows,Celestial Pearl danios,Sparkling Gourami, Otocinclus,and German blue and Gold rams are a few other fish who do best with nitrates kept at levels below 40 ppm. Always best in my view,, to aim for 20 ppm.

gammahermit 04-06-2009 07:23 AM

So the reason for water changes is to remove the built up nitrates & to replenish the minerals used by the fish. According to my testing kit hardness is the measure of calcium & magnesium & they are need by the fish to maintain correct balance between its internal body fluid & the external environment. So if the hardness is at appropriate levels is it still necessary to replenish the minerals or are there other minerals that the fish need.

Also I am not trying to argue against water changes. I am just trying to understand the reason for it is needed & to be able to determine when it is necessary to do so.

1077 04-06-2009 07:41 AM

I believe you pretty much understand it. Nearly all recommend weekly 20 to 25 percent water changes for long term health of fish in moderately stocked aquariums.

gammahermit 04-06-2009 08:08 AM

1 Attachment(s)
I would like to determine how often changes are required for my tank. From this discussion it seem that nitrate levels & hardness should be used to determine when a water change is needed. At what values should I change the water. I have been recording the measurements for the last 80 days & graphed them & attached it to this post. the horizontal axis is the number of days since january 1st.

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