At what tank size does dosing become more financially viable than weekly water changes?

TheoScapes · Jan 12, 2023

Hey all,

I was wondering if any of you experienced reefers have done the math on / gone through this:

At what tank size does it become cheaper to replenish lost nutrients through dosing rather than weekly or biweekly water changes?

I know there's a whoople bunch of things to take into consideration (such as nitrate and phosphate removal/ levels, the presence of a fuge, size of the protein skimmer, calcium reactors, etc), so let's for the sake of this discussion go with the following basic setup as I believe this will cover the largest target audience:

- skimmer fit to size
- refugium
- filter socks changed weekly

I'm curious as I acknowledge the benefits of water changes to keep levels stable I'm smaller setups, but is it really as beneficial in larger setups given that some nutrients deplete much slower than others?
I mean if I'm doing the weekly water change just to replenish alkalinity and/or even calcium, am I not essentially discarding perfectly good magnesium, strontium, and other micros and essentially wasting 80% of perfectly good water in order to replace 20% of bad water?

This seems silly to me, but I could be completely wrong, hence the question. Hoping to learn from you.

Happy reefing.

T

Lost in the Sauce · Jan 12, 2023

Too many variables to have a set number.

Water change percentage
Cost of making/buying water
Cost of dosing equipment
Ongoing dosing cost

Are the big ones..

MNFish · Jan 12, 2023

I dose my 13.5 gallon and went 6 months without a water change and it was bullet proof. I just use the AFR mix yourself and a Kamoer doser. But that will not work for everyone, normally even though I dose all 3 of my reefs I still do small to sometime medium water changes.

I think the number depends more on how much your reef tank consume than the size a new aquarium might be able to go perfect for 6 months on just water changes. However once growth starts you then you will consume more than water changes can effectively replace unless you plan to do them daily. Dosing helps not only to replenish but to keep stable which in a lot of ways is priceless.

SpyC · Jan 12, 2023

It's less about tank size and more about whay your tank is consuming. A 20g tank filled with clams and bony corals will consume more than a 200g tank with softies.

TheoScapes · Jan 12, 2023

Thanks for all your responses.

For the sake of the continuation of this discussion, let's add the following assumptions to the research question:

- water changes are 15%
- salinity is kept at 1.026
- it is a mixed reef with a balanced amount of soft, LPS, and SPS.
- RODI system available
- RS purple bucket salt

I know getting a difinitive answer would be improbable/ impossible, but it does merit a discussion and I was wondering if anyone else had gone through this thought process.

T

MNFish · Jan 12, 2023

This is something I put together when all for reef mix youself just came out and you can use 1 kamoer dosing pump to run it. Could probably make the same sort of thing with a salt mix for each one at 15% and see how it ends up

Tank Size	13.5
Number of Liters	10
Price	68.4
Milliliter	10000
Price per Milliliter	0.00684
Min Dose per gallon Milliliter	0.192308
Daily cost Min Dose	0.017758
Max Dose per gallon Milliliter	0.961538
Daily cost Max Dose	0.088788

Tank Size	32
Number of Liters	10
Price	68.4
Milliliter	10000
Price per Milliliter	0.00684
Min Dose per gallon Milliliter	0.192308
Daily cost Min Dose	0.042092
Max Dose per gallon Milliliter	0.961538
Daily cost Max Dose	0.210462

Tank Size	55
Number of Liters	10
Price	68.4
Milliliter	10000
Price per Milliliter	0.00684
Min Dose per gallon Milliliter	0.192308
Daily cost Min Dose	0.072346
Max Dose per gallon Milliliter	0.961538
Daily cost Max Dose	0.361731

Tank Size	75
Number of Liters	10
Price	68.4
Milliliter	10000
Price per Milliliter	0.00684
Min Dose per gallon Milliliter	0.192308
Daily cost Min Dose	0.098654
Max Dose per gallon Milliliter	0.961538
Daily cost Max Dose	0.493269

Q

ilikefish69 · Jan 12, 2023

Science

MNFish · Jan 12, 2023

Tank Size	13.5
%water change	15
Water changed	2.025
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	1.152934
Daily price of water change	0.164705


Tank Size	20
%water change	15
Water changed	3
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	1.70805
Daily price of water change	0.244007


Tank Size	55
%water change	15
Water changed	8.25
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	4.697138
Daily price of water change	0.67102


Tank Size	75
%water change	15
Water changed	11.25
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	6.405188
Daily price of water change	0.915027

MNFish · Jan 12, 2023

Tank Size	13.5
%water change	15
Water changed	2.025
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	1.152934
Daily price of water change	0.164705


Tank Size	32
%water change	15
Water changed	4.8
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	2.73288
Daily price of water change	0.390411


Tank Size	55
%water change	15
Water changed	8.25
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	4.697138
Daily price of water change	0.67102


Tank Size	75
%water change	15
Water changed	11.25
Price of salt	113.87
Gallons of salt	200
Price per gallon	0.56935
Price of water change	6.405188
Daily price of water change	0.915027

MNFish · Jan 12, 2023

This is for tropic marin salt with a price of 113 for a 200 gallons

MNFish · Jan 12, 2023

I added the salt one if you want to change the tank sizes or price of salt

MNFish · Jan 12, 2023

Just looking at the numbers it appears dosing with all for reef is 1/2 as much as water changes with tropic marin salt, however if you used a cheaper salt you might be able to break even.

MNFish · Jan 12, 2023

My kitten helped with the math.

TheoScapes · Jan 12, 2023

MNFish said:
My kitten helped with the math.

Thanks for all the information and for doing the math. Sure the reefing community could benefit greatly from what you've shared here.

V A R I A N T · Jan 12, 2023

Time and manual lift could be other considerations, and if you travel, in favor of dosing vs water changes. Putting out there for additional thought.

Daniel@R2R · Jan 13, 2023

SpyC said:
It's less about tank size and more about whay your tank is consuming. A 20g tank filled with clams and bony corals will consume more than a 200g tank with softies.

This is essentially what I came in here to say.