Continous waterchanges

Cory · Nov 10, 2016

I want to set up a tank that runs on continuous water changes. In a 20 gallon, how much daily would keep the water perfect? 60%? Main concern is to keep algae growth nearly non existent.

saltyphish · Nov 10, 2016

60% daily seems excessive to me. Depending on feedimg habits i would think 10% is plenty. Even that seems a bit much to me.

Cory · Nov 10, 2016

saltyphish said:
60% daily seems excessive to me. Depending on feedimg habits i would think 10% is plenty. Even that seems a bit much to me.

The system wouldnt have any filtration just continous water changes. The fish load would be 4 chromis, and one clown goby.

ebushrow · Nov 10, 2016

do you plan on having water circulation in the tank? I agree if you do that IMO at 60%, this is excessive...I would say 10% a day as long as you dont have corals.

Cory · Nov 10, 2016

ebushrow said:
do you plan on having water circulation in the tank? I agree if you do that IMO at 60%, this is excessive...I would say 10% a day as long as you dont have corals.

Yes it will have coral. Mixed reef. Low alk demand.

Randy Holmes-Farley · Nov 10, 2016

Cory said:
I want to set up a tank that runs on continuous water changes. In a 20 gallon, how much daily would keep the water perfect? 60%? Main concern is to keep algae growth nearly non existent.

Perfect is not attainable.

30-50% daily will keep alkalinity in a reasonable level. I show that in the article below.

How high prevents algae is not something that can be stated, IMO, with any accuracy.

If you assume a tank that might, without changes, accumulate 0.1 ppm nitrate daily, here's what different levels of continuous water changes accomplish:

Water Changes in Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-10/rhf/index.php

from it:

Figure 12. Nitrate concentration as a function of time when performing daily water changes equivalent to 0% (no changes), 7.5%, 15% and 30% of the total volume each month (in other words, 0%, 0.25%, 0.5% and 1% per day). In this example, nitrate is present at 100 ppm at the start, and is accumulated at a rate of 0.1 ppm per day when no water is changed.

Randy Holmes-Farley · Nov 10, 2016

Or if you start with no nitrate:

http://reefkeeping.com/issues/2005-10/rhf/index.php

Figure 8. Nitrate concentration as a function of time when performing daily water changes equivalent to 0% (no changes), 7.5%, 15% and 30% of the total volume each month (in other words, 0%, 0.25%, 0.5% and 1% per day). In this example, nitrate is present at 0 ppm at the start, and is accumulated at a rate of 0.1 ppm per day when no water is changed.

TheEngineer · Nov 10, 2016

These numbers only account for removal of nitrates via water change, correct? They do not account for removal by nitrifying bacteria? Or is the rate limited to a 0.1ppm increase due to all other elimination methods?

Paul B · Nov 10, 2016

Constant water changes may make more algae grow, not less. The most algae grows in new tanks with new water. IMO, not a good idea.

Randy Holmes-Farley · Nov 10, 2016

icecool2 said:
These numbers only account for removal of nitrates via water change, correct? They do not account for removal by nitrifying bacteria? Or is the rate limited to a 0.1ppm increase due to all other elimination methods?

It assumes that nitrate would otherwise accumulate at 0.1 ppm per day (i.e., with no water changes) , regardless of how much nitrifying, denitrifying and other nitrogen processing steps might be taking place.

Cory · Nov 10, 2016

Too bad its uncertain about limiting algae growth.

Randy Holmes-Farley · Nov 10, 2016

The only scenario where I can see it boosting algae is if the tank algae growth is limited by iron or other trace elements that are not being added except by water change.

TheEngineer · Nov 10, 2016

What about organics/silicates in the water source?

Is silicate an organic?

Randy Holmes-Farley · Nov 10, 2016

icecool2 said:
What about organics/silicates in the water source?

Is silicate an organic?

No it isn't, but a properly working RO/DI will remove both of them.

So I should qualify the statement to mean purified source water.

Cory · Nov 10, 2016

What if all uneaten food and poop is removed continously too? Algae growth will die off? Some how ill make it drain the poop and food out.

Randy Holmes-Farley · Nov 11, 2016

Cory said:
What if all uneaten food and poop is removed continously too? Algae growth will die off? Some how ill make it drain the poop and food out.

That would certainly help reduce nutrients.

Larry L · Nov 11, 2016

Relying solely on continuous water changes for maintaining levels seems like kind of an expensive approach to me, compared to using any of the typical dry 2-part mixes.