Auto water change and dosing

[coweyes298]

I am currently dosing 2 parts using APEX DOS on my main display tank.
ALK solution is at 90 ml per day. Cal is the same amount. Display tank total water volume is 120 gallon with minimum coral. But I do have huge amount of coralline algae on my rock. This dosing amount gives me stable calcium and alkalinity number.

Since I have a separate small coral frag tank and I am doing auto water change on that tank, I am getting stable parameter and there is no need to dose 2 parts. That frag tank does have several acro and other sps lps mixed in. The amount of water change for the frag tank is about 0.7 gallon a day. Total volume of frag tank is 11 gallon.

Does anyone know if AWC can replace the 2 parts dosing totally? I am afraid with 120 gallon system with auto water change at 1 % daily you will still need to dose 2 parts to supplement the element. That also means I need to source another dosing pump....

 

[JoshH]

I read somewhere saying that AWC can never replace dosing once your tank gets to the point (or even before that) that you need to dose. I believe it was something to do with the triton method which works off the basis that Water changes are essentially not worth it. Unless you do a 100% WC say over the course of a day or two, you're only replacing a fraction of whats being consumed. I'll have to do some digging to see if I can find it again.

 

[Randy Holmes-Farley Verified Community Expert]

I am currently dosing 2 parts using APEX DOS on my main display tank.
ALK solution is at 90 ml per day. Cal is the same amount. Display tank total water volume is 120 gallon with minimum coral. But I do have huge amount of coralline algae on my rock. This dosing amount gives me stable calcium and alkalinity number.

Since I have a separate small coral frag tank and I am doing auto water change on that tank, I am getting stable parameter and there is no need to dose 2 parts. That frag tank does have several acro and other sps lps mixed in. The amount of water change for the frag tank is about 0.7 gallon a day. Total volume of frag tank is 11 gallon.

Does anyone know if AWC can replace the 2 parts dosing totally? I am afraid with 120 gallon system with auto water change at 1 % daily you will still need to dose 2 parts to supplement the element. That also means I need to source another dosing pump....

It cannot, unless the demand is VERY low, or the AWC is very high.

A typical reef tank would need 30-50% changed daily to meet the demand.

I show that here:

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

from it:

Very Large Water Changes Maintain Calcium and Alkalinity

In the previous section I showed that normal water changes of up to 30% per month cannot maintain calcium and alkalinity in reef aquaria. But at some point, large enough water changes can do so. What volume of water change is necessary to maintain calcium and alkalinity in reef aquaria? In a tiny aquarium, 3 gallons for example, large daily water changes might be acceptable. How large is required? Figure 23 shows the drop in alkalinity for a low demand aquarium changing 0%, 5%, 10%, 15% and 30% of the water EVERY DAY. In that case, it appears to require between 10% and 30% of the total water volume to be changed every day to maintain suitable alkalinity. Figure 24 shows similar data for a higher demand aquarium (1 meq/L alkalinity per day). In this case, it takes close to a 50% water change each day to maintain suitable alkalinity. Similar data are obtained for calcium (not shown), where 30% and 50% daily water changes in a high demand aquarium (24 ppm calcium per day) stabilize at 364 and 396 ppm calcium, respectively. So, while changing 50% per day is really out of the question for any normal to large reef aquarium without an inlet directly from the ocean or a large seawater well, a 3-gallon nanoreef aquarium attached to a very slow continuous pump could maintain adequate calcium and alkalinity by replacing 1.5 gallons each day.