Cost of Water Changes Vs Dosing in Maintaining Calcium and Alkalinity

[Randy Holmes-Farley]

In a recent thread, the topic came up whether it is cheaper to maintain calcium and alkalinity by water change or by dosing.

Water changes are always far more expensive, as seen below, although folks may be doing them for other reasons anyway, in which case one might consider it to be free.

I thought I’d start a separate thread to record some calculations to show how much cheaper dosing is than water changes.

Note that the relative result is independent of tank size, but this calculation says nothing about ease of doing either one nor am I making a claim about what is best to do (which may vary by tank size).

I will assume a 100 gallon total water volume system, and will look at alk rises from 7 dKH to 8, 9, or 10 dKH. Folks can scale the results to whatever size interested then.

I will choose a top end supplement, ESV B-ionic and a high end high alk salt mix, Red Sea Coral Pro. As a note, the higher the alk in the salt mix the less is needed, hence the choice of a high alk mix to reduce it’s apparent costs.

Right now, BRS sells 1 gallon ESV B-ionic mixes for $33.14 and a 200 gallon Coral Pro container for 79.99. No cost is added for the RO/di to make the salt mix.

Assuming the salt mix has 12 dKH as Red Sea claims, then it takes the following:

7-8 dKH, 20% change, 20 gallons needed, $8.00 cost

7-9 dKH, 40% change, 40 gallons needed, $16.00 cost

7-10 dKH, 60% change, 60 gallons needed, $24.00 cost

Doing a similar calculation for the ESV, we find that a 1 dKH boost takes 48.3 mL. That gives use these results:


7-8 dKH, 48.3 mL, $0.42 cost
7-9 dKH, 96.6 mL, $0.85 cost
7-10 dKH, 144.9 mL, $1.27 cost

We can see from these calculations that the cost of maintaining alk in these two ways is 19 times higher when accomplishing it by water change.

 

[GobyGuy]

Have you done any research or writing on no water change reefs / reef moonshiners methods

 

[areefer01]

You noted 'No cost is added for the RO/di to make the salt mix' but in some areas that could be a high cost due to water rates. Not to mention environmental impact by RO/di waste.

Then again thinking on it your numbers just present dollars and sense as it relates to maintenance. No need for the other noise.

Thanks for the post and hope your day is going well.

 

[Randy Holmes-Farley]

Have you done any research or writing on no water change reefs / reef moonshiners methods

Only in posts, not in an article. My three concerns are:

1. Setting optimal target levels for dosing is not trivial, but is not worse here than other methods.

2. ICP accuracy as used by reefers.

3. How to deal with accumulating chemicals, whether those might be organic or inorganic.

 

[Daniel@R2R]

Interesting info! Thanks Randy!

 

[Dan_P]

In a recent thread, the topic came up whether it is cheaper to maintain calcium and alkalinity by water change or by dosing.

Water changes are always far more expensive, as seen below, although folks may be doing them for other reasons anyway, in which case one might consider it to be free.

I thought I’d start a separate thread to record some calculations to show how much cheaper dosing is than water changes.

Note that the relative result is independent of tank size, but this calculation says nothing about ease of doing either one nor am I making a claim about what is best to do (which may vary by tank size).

I will assume a 100 gallon total water volume system, and will look at alk rises from 7 dKH to 8, 9, or 10 dKH. Folks can scale the results to whatever size interested then.

I will choose a top end supplement, ESV B-ionic and a high end high alk salt mix, Red Sea Coral Pro. As a note, the higher the alk in the salt mix the less is needed, hence the choice of a high alk mix to reduce it’s apparent costs.

Right now, BRS sells 1 gallon ESV B-ionic mixes for $33.14 and a 200 gallon Coral Pro container for 79.99. No cost is added for the RO/di to make the salt mix.

Assuming the salt mix has 12 dKH as Red Sea claims, then it takes the following:

7-8 dKH, 20% change, 20 gallons needed, $8.00 cost

7-9 dKH, 40% change, 40 gallons needed, $16.00 cost

7-10 dKH, 60% change, 60 gallons needed, $24.00 cost

Doing a similar calculation for the ESV, we find that a 1 dKH boost takes 48.3 mL. That gives use these results:


7-8 dKH, 48.3 mL, $0.42 cost
7-9 dKH, 96.6 mL, $0.85 cost
7-10 dKH, 144.9 mL, $1.27 cost

We can see from these calculations that the cost of maintaining alk in these two ways is 19 times higher when accomplishing it by water change.

You seem to have left no opportunity for this post to become 20 pages of replies and debates

 

[MorganAtlanta]

I don't know anyone who tries to manage Alk by water changes. That would be insane-- a 20-40% daily water change? That said, it would be interesting to see how much water you would have to change daily to maintain calcium, and if not calcium, then magnesium.

 

[Randy Holmes-Farley]

I don't know anyone who tries to manage Alk by water changes. That would be insane-- a 20-40% daily water change? That said, it would be interesting to see how much water you would have to change daily to maintain calcium, and if not calcium, then magnesium.

Done. Lol

Water Changes in Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

 

[MorganAtlanta]

Thanks!

 

[Randy Holmes-Farley]

You’re welcome.

Happy Reefing!

 

[Idech]

Very interesting, thank you !

 

[killer2001]

How about a cost of doing water changes vs dosing everything required to simulate a water change, including carbon dosing for nutrient reduction and all trace elements to acceptable values. (I guess step one would be creating a thorough list of EVERYTHING a water change does or can do).

 

[spicymikey]

Good article. I like cost analysis studies. Of course time is money, as they say , so if we want to factor in effort to the cost equation then the answer is likely not as simple . You mentioned effort in your posting and I caution people to seriously consider that as well. Many times people get into this reefing hobby and underestimate effort more than hard costs. To me it seems like the number one reason people get out of the hobby as well. Not only are you showing that hard costs are higher doing water changes, but also, imo, water changes become less practical the larger the system gets. I suppose it depends on what you consider large, and everyone's threshold is different. But for me I draw the line at around 100+ gallons. If you can afford the upfront expense of automated monitoring and dosing equipment, like an apex, then the ongoing operating expense (and effort) is going to be significantly less doing dosing. Long-term you will spend less time and effort which will no doubt make you a happier reefer. Thanks again for the cost analysis Randy

 

[92Miata]

How about a cost of doing water changes vs dosing everything required to simulate a water change, including carbon dosing for nutrient reduction and all trace elements to acceptable values. (I guess step one would be creating a thorough list of EVERYTHING a water change does or can do).

"Everything" is pretty much impossible to assess here.

But if you look at carbon dosing, calcium, alkalinity, magnesium, and something like Red Sea trace - it's still going to be significantly cheaper than water changes (and that's using stuff like ESV). All of these are orders of magnitude cheaper than salt.

If you get into bulk products (like straight Sodium BiCarbonate, Calcium Chloride, Magnesium Chloride/Sulfate mix, etc) - it's going to be waaaaay cheaper. There's enough in a $.99 box of baking soda to make almost 2 gallons of the alkalinity part of Randy's improved 2 part recipe - which is 2660 dKH - so roughly 5000 dKH-gallons.


Depending on brand, there's about 900 (TM-Pro) -1500 (RC) dkh-Gallons in a bucket of salt ($40-100)

Good article. I like cost analysis studies. Of course time is money, as they say , so if we want to factor in effort to the cost equation then the answer is likely not as simple . You mentioned effort in your posting and I caution people to seriously consider that as well. Many times people get into this reefing hobby and underestimate effort more than hard costs. To me it seems like the number one reason people get out of the hobby as well. Not only are you showing that hard costs are higher doing water changes, but also, imo, water changes become less practical the larger the system gets. I suppose it depends on what you consider large, and everyone's threshold is different. But for me I draw the line at around 100+ gallons. If you can afford the upfront expense of automated monitoring and dosing equipment, like an apex, then the ongoing operating expense (and effort) is going to be significantly less doing dosing. Long-term you will spend less time and effort which will no doubt make you a happier reefer. Thanks again for the cost analysis Randy

This is really a question of system design. In a properly designed larger system, water changes are incredibly simple. I was maintaining a 20K gallon FO saltwater tank for a while - and it was basically switches and buttons. Easier than doing 10 gallons on my own small tank.

The water change reservoir would fill itself automatically, and had its own circulation pumps. I think it was 2500 gallons?

I'd dump several boxes of salt into a hopper that would drain into the reservoir over an hour or so.

When it was mixed, I'd flip a couple of valves - this would cause the tank to drain down - and the standpipe used for this was set to precisely the height where volume drained matched the water change reservoir. When water stopped flowing out the drain, I'd close the valves.

I'd then hit a button, and the water change reservoir would get pumped into the tank. When the pump ran dry, it would turn itself off, and trigger the RO unit to start refilling the reservoir.


Probably 5 minutes actual work to change thousands of gallons.

 

[Randy Holmes-Farley]

How about a cost of doing water changes vs dosing everything required to simulate a water change, including carbon dosing for nutrient reduction and all trace elements to acceptable values. (I guess step one would be creating a thorough list of EVERYTHING a water change does or can do).

I address what a water change can do in the linked article, but a cost analysis of everything would be impossible since there’s no fixed need or salt mix level of all of these things.

 

[Spare time]

Only in posts, not in an article. My three concerns are:

1. Setting optimal target levels for dosing is not trivial, but is not worse here than other methods.

2. ICP accuracy as used by reefers.

3. How to deal with accumulating chemicals, whether those might be organic or inorganic.

As for #3, what chemicals are you most concerned with building up? Would quality carbon in a reactor alleviate some of your concerns? In my no water change tank, after using an ATI icp test, I ran some cuprisorb for a little to help with some metals that appeared to be elevated ( I am not sure about the error margin in the ATI icp).

 

[DavidinGA]

Now add in a 3rd option of dosing KALK and show how expensive dosing 2 part is by comparison! lol



...actually I'll do some of the math for ya...

Mrs Wages Pickling lime is about $4 per 16oz bag.
16oz is good for about 96 teaspoons.
$4 divided by 96 teaspoons is approximately $0.04 per tsp.
2tsp per gallon for saturated kalk, so $0.08 per gallon of end-use product.

For the above example on a 100g system and you want to raise your ALK from 7 to 8 you would need 112fl oz of KALK or a grand total cost of $0.07!

For perspective dosing the 2 part from the original example is SIX times more expensive than using KALK, not to mention you are also getting CAL and a pH boost essentially for free since the 2-part example from above is the cost to only dose ALK.

 

[92Miata]

Now add in a 3rd option of dosing KALK and show how expensive dosing 2 part is by comparison! lol



...actually I'll do some of the math for ya...

Mrs Wages Pickling lime is about $4 per 16oz bag.
16oz is good for about 96 teaspoons.
$4 divided by 96 teaspoons is approximately $0.04 per tsp.
2tsp per gallon for saturated kalk, so $0.08 per gallon of end-use product.

For the above example on a 100g system and you want to raise your ALK from 7 to 8 you would need 112fl oz of KALK or a grand total cost of $0.07!

For perspective dosing the 2 part from the original example is SIX times more expensive than using KALK, not to mention you are also getting CAL and a pH boost essentially for free since the 2-part example from above is the cost to only dose ALK.

Yes, dosing ESV is more expensive than Miss Wages - that's not a factor of 2-part vs Kalk though - its a factor of an aquarium specific premium product vs a cheap bulk grocery product.

When you're looking at bulk products of similar quality - they're not significantly different, and it fluctuates based on commodity prices. If you're worried about cheapest cost per dkH - buy a calcium reactor. They're way cheaper to run.

 

[Randy Holmes-Farley]

As for #3, what chemicals are you most concerned with building up? Would quality carbon in a reactor alleviate some of your concerns? In my no water change tank, after using an ATI icp test, I ran some cuprisorb for a little to help with some metals that appeared to be elevated ( I am not sure about the error margin in the ATI icp).

My biggest concerns for most tanks are organics that don’t bind to GAC and the commercial resins folks use, and there is little to no dats on which organics any of these methods bind in a reef tank.

Accumulations of some inorganic ions are also a concern, especially if you do not get quality icp testing, but even if you do, water changes might be the best way to reduce them.

 

[Randy Holmes-Farley]

Now add in a 3rd option of dosing KALK and show how expensive dosing 2 part is by comparison! lol



...actually I'll do some of the math for ya...

Mrs Wages Pickling lime is about $4 per 16oz bag.
16oz is good for about 96 teaspoons.
$4 divided by 96 teaspoons is approximately $0.04 per tsp.
2tsp per gallon for saturated kalk, so $0.08 per gallon of end-use product.

For the above example on a 100g system and you want to raise your ALK from 7 to 8 you would need 112fl oz of KALK or a grand total cost of $0.07!

For perspective dosing the 2 part from the original example is SIX times more expensive than using KALK, not to mention you are also getting CAL and a pH boost essentially for free since the 2-part example from above is the cost to only dose ALK.

I certainly ageee limewater can be super cheap. I had a 50 pound bag of Mississippi Lime Company calcium oxide that was about $20 (IIRC), but that was a long time ago. It lasted many years in my tank.