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post #1 of 25 (permalink) Old 12-04-2014, 09:15 PM Thread Starter
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water change frequency

Hi all! Is it ok to do frequent small water changes rather than one large one?
I have an 80 gallon, excel, moderately planted and stocked. I would do maybe 1 to 2 gallons every other day for a total of 12 to 15 gallons per week.
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post #2 of 25 (permalink) Old 12-04-2014, 10:38 PM
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The answer depends on why are you doing water changes.
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post #3 of 25 (permalink) Old 12-04-2014, 10:51 PM
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http://reefkeeping.com/issues/2005-10/rhf/#10

This is a very excellent read. Essentially small continuous water changes are just as efficient as large waterchanges at reducing toxic compounds.
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post #4 of 25 (permalink) Old 12-04-2014, 10:53 PM
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If you decided that this "moderately" stocked tank was so by putting your fish into the AqAdvisor and it said 50 or 60 % on the stocking, the plants may use up enough nitrates for that to work.
Normally it is not enough.
You will get better results to not only do all the water change at one time but also to do a higher percent of it. Some of the shrimp people use far less water change but they usually have only shrimp in their tanks so very low bio-load.
You can test to see what effect your style of water change has done so far by just testing for Nitrates.

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post #5 of 25 (permalink) Old 12-04-2014, 11:40 PM
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If you do 2 gallon water changes every day for a week that does not add up to 14 gallons of water changed.

The math is easier if you think of it this way:
Lets start the tank with 40ppm NO3
If you changed 100% of the water there would be no more nitrates in the tank.
If you changed 50% of the water there would be 20ppm NO3.
If you then turned right around and did another 50% water change does this equal a 100% water changes? No. You would end up with 10ppm NO3.

So: 2 x 50% is not equal to 100%, but is equal to 75%.

Anyway, changing a couple of gallons a day could be very worthwhile, if you are siphoning the gallon or two out of a stagnant spot that tends to accumulate debris. Also, using the water removed from the tank to clean the filter media.
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post #6 of 25 (permalink) Old 12-05-2014, 03:15 AM
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And the other thing to consider is the nitrate levels in your replacement water. For instance, my tap water has about 10 ppm nitrates so, in my case, that would change Diana's math a bit. I dose EI but instead of changing 50% once a week I've found that my fauna seems to do better if I change 20 to 25% twice a week.
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post #7 of 25 (permalink) Old 12-05-2014, 03:28 AM
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It would depend on a lot of things. animal waste, plant density, filter size, and how much food you add.
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post #8 of 25 (permalink) Old 12-05-2014, 09:36 AM
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Quote:
Originally Posted by Raul-7 View Post
http://reefkeeping.com/issues/2005-10/rhf/#10

This is a very excellent read. Essentially small continuous water changes are just as efficient as large waterchanges at reducing toxic compounds.
I'd take the information in this article with a grain of salt since it's geared towards salt water reef tanks. In reef tanks, even the slightest change in pH or salinity will wreck havoc on your tank. Freshwater tanks with the exception of your fancy shrimp tanks are less sensitive to large water changes.

Mathematically one large 30% water change will always remove more toxins than multiple water changes that add up to "30%" e.g. 1 30% WC will remove more toxins than 3 10% water changes. (30% toxin removal vs. 1-0.9^3=27.1% toxin removal).

ADA 120P, DoAqua 90P, ADA 60P, ADA 30C x2, ADA 45P, ADA Mini-M
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post #9 of 25 (permalink) Old 12-05-2014, 01:21 PM Thread Starter
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Thanks, lots of good information to think about. I found the aqadvisor, nice site. I am 62% stocked and have 1342% filtration capacity. The site recommended an 18% water change schedule. Can I still split this into twice a week; if too large I have trouble handling the heavy buckets.
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post #10 of 25 (permalink) Old 12-05-2014, 06:46 PM
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2 gallons out of 80 gallons is only 2.5% of the water being changed at a time. I think that means it takes 27 of those water changes to remove half of the original water. That means you would be changing half the water every 6 weeks, at best. I don't think that will be very effectiive.

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post #11 of 25 (permalink) Old 12-05-2014, 11:57 PM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
2 gallons out of 80 gallons is only 2.5% of the water being changed at a time. I think that means it takes 27 of those water changes to remove half of the original water. That means you would be changing half the water every 6 weeks, at best. I don't think that will be very effectiive.
Whoa, the math sure made that real! I will up my water changes for sure.
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post #12 of 25 (permalink) Old 12-06-2014, 12:41 AM
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Playing devils advocate. What if a planted tank never had water changes but only water added as it evaporated, what are the ramifications?
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post #13 of 25 (permalink) Old 12-06-2014, 07:42 AM
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Presuming Fauna...life expectancy inversely proportioned to the stocking percent. The "system" of nature is typically populated by a bio-load which has a decimal point in front of it.
IMO...

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Last edited by Raymond S.; 12-06-2014 at 07:58 AM. Reason: The "system"...
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post #14 of 25 (permalink) Old 12-06-2014, 02:02 PM
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Quote:
never had water changes but only water added as it evaporated
We can follow what happens in my tanks.
While I do not follow the 'never' water changes, sometimes I do go for a while with only topping off. Lets just follow the TDS (Total Dissolved Solids)

Tap water:
TDS = upper 200s, usually between 250-280

Tank, right after a water change (assume 100%) is matching the tap water.
Some water evaporates, but it does not take the minerals with it. I add more tap water (and therefore more minerals). The plants are using a very small amount of these minerals. Not enough to really drop the levels.
TDS rises.
Over a week or a month the amount is not much, and a big water change (50%) would reset it to match (or nearly match) the tap with no strain on the fish.
Over several months it keeps adding up, though.
By the end of the summer the lowest TDS I can find in any tank is in the upper 300s, pretty close to 400. Most tanks are well into the 400s. Basically it has doubled.

In actual fact I am doing very small water changes. I am taking out enough water to clean the filters, perhaps once a month. A couple of gallons cleans most filters. This is easily 20% on the smaller tanks, but not even 10% on the larger tanks. And the TDS is climbing...

The GH is rising, too. The KH is different because I have some substrates that remove it. I am not replacing enough water to keep the KH up. So it drops, and this allows the pH to drop.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To do larger water changes get away from the buckets.
I have several garbage cans. When I was doing 50% per week, every week on about 20 tanks I would fill the garbage cans with whatever water I needed (Tanks had different water chemistries from black water & RO to low end brackish) and use pumps.
A siphon (gravel vac) to get the water out into a bin on the floor. Clean the filter in that. Keep siphoning more water out of the tank. Pump and garden hose got the dirty water out to the garden.
New water added to the tank from the garbage can via pump.
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post #15 of 25 (permalink) Old 12-06-2014, 03:15 PM Thread Starter
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Quote:
Originally Posted by Diana View Post
We can follow what happens in my tanks.
While I do not follow the 'never' water changes, sometimes I do go for a while with only topping off. Lets just follow the TDS (Total Dissolved Solids)

Tap water:
TDS = upper 200s, usually between 250-280

Tank, right after a water change (assume 100%) is matching the tap water.
Some water evaporates, but it does not take the minerals with it. I add more tap water (and therefore more minerals). The plants are using a very small amount of these minerals. Not enough to really drop the levels.
TDS rises.
Over a week or a month the amount is not much, and a big water change (50%) would reset it to match (or nearly match) the tap with no strain on the fish.
Over several months it keeps adding up, though.
By the end of the summer the lowest TDS I can find in any tank is in the upper 300s, pretty close to 400. Most tanks are well into the 400s. Basically it has doubled.

In actual fact I am doing very small water changes. I am taking out enough water to clean the filters, perhaps once a month. A couple of gallons cleans most filters. This is easily 20% on the smaller tanks, but not even 10% on the larger tanks. And the TDS is climbing...

The GH is rising, too. The KH is different because I have some substrates that remove it. I am not replacing enough water to keep the KH up. So it drops, and this allows the pH to drop.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To do larger water changes get away from the buckets.
I have several garbage cans. When I was doing 50% per week, every week on about 20 tanks I would fill the garbage cans with whatever water I needed (Tanks had different water chemistries from black water & RO to low end brackish) and use pumps.
A siphon (gravel vac) to get the water out into a bin on the floor. Clean the filter in that. Keep siphoning more water out of the tank. Pump and garden hose got the dirty water out to the garden.
New water added to the tank from the garbage can via pump.
Nice water change system, but a bit harder in a small condo with new hardwood floors in Michigan! I am thinking of how to rig something like that, however. Thanks for the info.
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