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Discussion Starter · #1 ·
Background: I have had atleast one aquarium continuously since the mid 80's. Both fresh and saltwater setups with a maximum of 13 tanks at once. I've made plenty of mistakes along the way all the while establishing what works for me and the tanks inhabitants.

Given: The keeping of fish by home aquarists seems to be as much art as it is science.

Recently I established a 150g African Cichlid tank. That is why I found this forum. Lately I have been giving much thought to the frequency and quantity of water to change out of the system which led me to the following observation. I made the following caculations this morning regarding partial water changes:

25% weekly wc is equivalent to a 50% monthly wc and 2X contaminates remain,
50% weekly wc is equivalent to a 75% monthly wc and 1X contaminates remain,
75% weekly wc is equivalent to a 92% monthly wc and 0.33X contaminates remain.

Where X = weekly contanimemts (ie. Nitrates and other pollutants)

Ideally a continuous wc would be best for the tanks inhabitants.
 

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Discussion Starter · #2 ·
So my question is this. Even with consistent moderate partial water changes in a closed system won't pollutants (ie. nitrates) build up to an unacceptable level?

Thoughts, comments and/or observations are welcomed.
 

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Could you explain this please. I don't mean to sound rude but this makes absolutely no sense at all to me. How does 25% weekkly = 50% monthly?
 

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Discussion Starter · #4 ·
Basically what I am attempting to convey is that if you performed 25% weekly water changes it would be roughly equivalent to doing a 50% monthly water change as measured by nitrates PPM.
 

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Your water change schedule should not be based on percentages alone. The amount of fish you have, and how well you vacuum waste out during WC's will affect nitrate buildup. You need to test your water before and after a WC and decide on your target nitrate range, I keep my tanks below 20ppm, some people don't mind 40 or even 60ppm. I have dtermined after these tests that a 40% weekly water change keeps my nitrates well below 20ppm, so that's the schedule I'm on.
 

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Aha, I see now. For what it's worth, I think small water changes are a complete waste of time. I take out aprox. 90g out of my 120's, 100g from my 210 and 30g from each of my 40s every sunday. Every now and then I do an additional midweek w/c to remove those nitrates that have crept up.
 

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Sorry to differ but I think you are trying too hard to make a standard out of a very flexible situation. There are so many things that vary over time, that applying some type of formula is not much better than guesswork. To apply a formula of this type would require much more precision in the tanks than I find. For some certain variables there are these to consider. The fish will grow, you will feed different amounts on different days, you will remove different amounts of waste when you vacuum, Your water will differ from summer to winter or other times and a biggie is that your filters will function differently when clean or dirty. All this boils down to taking a shot at being right, testing to see how it is working and adjust as needed.
 

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Cunados said:
So my question is this. Even with consistent moderate partial water changes in a closed system won't pollutants (ie. nitrates) build up to an unacceptable level?
PfunMo pointed out a lot of variables and is dead on, but in order to simplify things here's a simple formula that shows where your 'trates will max out.

N x 1/WC=Max Nitrates
(N being amount of nitrates produced and WC being percentage of water changed out, both variables being over the same time period, ie weekly or monthly).

As an example, say you do 1/3 water changes weekly, and your fish create 10ppm of nitrates every week. Nitrates will increase (even with water changes) until they hit 30. You then do a 1/3 change which takes out 1/3 of the nitrates, dropping you down to 20ppm, by next week it has gone up to 30, another water change brings it down to 20, etc.

Again, this is an oversimplified formula and doesn't take into account change in feeding, cleanliness of filters, build up of detrius in the tank, growth of fish, etc. But it shows that in theory water changes put a cap on the amount of nitrates in a closed system (which I think is what your question was asking). With a consistent routine (cleaning filters, vacuuming, etc) helps minimize the affect of other variables while regular checks on nitrate allow you to adjust for increase in bioload.
 

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But doing filter cleaning,swapping sponges, deep vacuum ,and algae scrubbing can bring nitrates lower then half if the same wc % is done. I see your point but this is why we test. If we just removed just the water then you would eventually get the constant raise in nitrates and pollutants .
 

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Flippercon said:
But doing filter cleaning,swapping sponges, deep vacuum ,and algae scrubbing can bring nitrates lower then half if the same wc % is done. I see your point but this is why we test. If we just removed just the water then you would eventually get the constant raise in nitrates and pollutants .
Not sure I agree with this to some point.

If you feed the same daily,and you do a certain percentage of a water change's regularly and the bio load has not changed, sure your nitrates might raise a bit but there should be some consistency to the levels if what your doing stays the same.

I think one thing this would prove is no tank is really the same.

It's like a hot tub which I sell and deal with water chem on a daily basis. Take 4 people in a 400 gallon spa, they use it at the same time every day, they use the same chems and monitor it on a daily basis. What is the variable is the size of the people, how much they sweat and the amount of filtration and what is on them at any given time. True a fish tank is different because fish don't react the same as people in hot water and the temp is quite a bit different as far as bacteria goes.

What I am getting at is every tank and every situation is different,from feeding, gallons of water in a tank and the number of fish. No way you can make what some else does to their tank unless it's exactly the same. Even then their are variables!
 

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I like the formulas, they help you set a standard. Yes, in a closed system (one where there is a constant, predictable build up of nitrates - as the OP indicated), the only change being your WC's, eventually, nitrates will build up more and more - but up to a point. At some point, there will be an equilibrium (this is what Duds pointed out) because of us changing water at a predictable rate (closed system, after all). This equilibrium is usually above what we desire.

see http://www.cichlid-forum.com/phpBB/viewtopic.php?t=223077&sid=8c7d849c5959995f0baf9f16eb5af387

We don't work with closed systems. We change filters, our fish produce more/less waste, we sometimes do 50% water changes every day for a week. I've even heard of the mythical 100% WC (fishies in a bucket, I assume). These extra large changes are needed exactly to curb that slow and steady rise of nitrates, and to 'reset' the trend to equilibrium.
 

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Nina_b
I have and will again do the "lay them flat 100% water change". If done right, it is beneficial for the fish.
 

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Number6 said:
Nina_b
I have and will again do the "lay them flat 100% water change". If done right, it is beneficial for the fish.
+1 and congrats for coming out and saying it. What seems to be missed here is that while every tank is in fact unique, doing more than the minimum water change keeps you ahead of the curve.
 

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There's a lot of confusion about the definition of minimum and maximum. When we change water we tend to think of the minimum as good enough. When we drive we tend to turn it upside down and use the maximum as the least we do. Maybe the fish aren't the source of the trouble! :p
 

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Discussion Starter · #15 ·
The previous postings is what I love about the net. Different perspectives and ideas.

Truth be known I hate testing water samples and would prefer a routine. But alas it is not good practice. A testing I will go.

Two things I found interesting are the 1) equillibrium point and 2) how much more water is consumed doing weekly vs. monthly WCs (twice as much water is used for 25% weekly vs. 50% monthly WCs).
 

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Cunados said:
The previous postings is what I love about the net. Different perspectives and ideas.
Agreed. Great discussion.

Here's another example...

For me a super large water change really isn't in the cards. I have 0.25ppm ammonia in my tap. The guys at my LFS, who really do know their stuff, recommend no more than 30% change unless it is an emergency.
 
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