Water changes-daily vs weekly?

[Randy Holmes-Farley Verified Community Expert]

Randy Holmes Farley has a new gig and said he would be offline more often for a bit so I will share something on this that I recall him discussing on another thread. He compared the daily automated water change method to larger weekly changes and said the improved efficiency of a weekly water change is minor. Something along the lines of about a 2% difference if memory serves correctly. He even had a formula comparing the two. He also said he prefers automated daily water changes for the stability (fewer alk swings, easier) benefits and that is what he ran himself in his own tank.

Thanks and yes.

 

[MARK M. DAVIS]

I recommend both

 

[MARK M. DAVIS]

I do both daily and monthly water changes. I used to do ONLY daily water changes of 1% tank volume 2.5 gallons / day x 6 days a week. I decided to augment with a 10%, 30 gallon, water change. The daily change didn't make much of a difference when it came to trace elements since depletion is greater than addition. The 10% is better because it provides more trace at one time but, I still need to dose specific elements like Iodine and Potassium with general trace at a reduced amount due to the 10% water change. (I test my water at Triton 4x a year). My alk and calcium consumption is large. Thus, I have to dose those with a calcium reactor. Water changes have negligible contributions. To eliminate things like Nitrates, most folks with high nitrates are not exporting and reducing importing. Thus, larger water changes are best since it has the largest single time impact but, it's only temporary since YOU have to reduce import (feeding, detritus accumulation, organics in the water, and contaminants) and export (algae scrubber, bio denitrator, other not as effective methods like chaeto and refugiums). The large water change may buy time for your coral but, is not a long term solution. For daily water changes, you don't have to worry about PH, temperature, alkalinity swings. The amount of change add is so negligible. Larger water changes >30% can be more stressful due to the changes in temperature, PH and alkalinity. That's too much work to match. Thus, 10% monthly is fine for me. No swings and no messing with heaters and alk supplement. The total for me is a 30% a month with no hassle. Hence, I do both methods. Now with regards to that article. Most of the charting compared a reduction in water change % for same amount of time. It give a good indicator of the effects of volume differences. I've noticed greater coral happiness after the 10% water change than when I was just doing daily.

 

[Randy Holmes-Farley Verified Community Expert]

I do both daily and monthly water changes. I used to do ONLY daily water changes of 1% tank volume 2.5 gallons / day x 6 days a week. I decided to augment with a 10%, 30 gallon, water change. The daily change didn't make much of a difference when it came to trace elements since depletion is greater than addition.

That's true on the one day you do the larger water change, but not the other 30 days of the month where the daily changes are trickling in trace elements.

FWIW, the last sentence is certainly very meaningful:

"I've noticed greater coral happiness after the 10% water change than when I was just doing daily."

Now with regards to that article. Most of the charting compared a reduction in water change % for same amount of time. It give a good indicator of the effects of volume differences.

FWIW, most of my graphs also compared daily vs monthly for the same total water changed in a month.

 

[2CC's]

Weekly changes are when I siphon/clean the sand a bit - not sure I would trade that away with daily changes.

 

[MARK M. DAVIS]

Randy, Alk, Ca are dosed with a calcium reactor and MG is dosed using an APEX DDR. I dose trace every two weeks. Iodine, Potassium, Strontium, amino acids, Iron twice a week for stability. The 10% water change once a month has a greater effect. (Just in case I'm over-doing the dosing or under-dosing, like a mini reset button). More than the daily. But, I certainly don't discount the daily. I continue daily, too, since it's already set up!!! Thanks for writing all of your very informative articles.

 

[beaslbob]

I do now!

"While lots of smaller changes (say, 30 changes of 1% each) are slightly less efficient than one larger one (30% in a single batch), the difference is small (30 changes of 1% each exactly matches one 26% batch water change), and consequently other factors of convenience or stress on organisms."

Was from Randy's article, posted above.

I'm an old guy so I repeat myself.

30 1% daily water changes will result in the same exact parameter just before the water change as a 30% water change every 30 days.

What will change are the parameters after the water change.

assuming a 1ppm/day increase.
_________________1%/day_______30%/30days
before water change____100ppm_______100ppm
after water change______99ppm________70ppm
before next change_____100ppm_______100ppm

 

[André Brasil]

@beaslbob I'm basically illiterate in the matter by experience - was just sharing what I read.

If I misinterpreted the article by the good doctor, it's my mistake.

 

[beaslbob]

@beaslbob I'm basically illiterate in the matter by experience - was just sharing what I read.

If I misinterpreted the article by the good doctor, it's my mistake.

no misinterpretation.

My analysis is based on where the system winds up at. Or to what final point is it going too. As opposed to all the "advanced" math with expended power functions which define where the system is at it goes along the path to that end point.

At the end point the amount of stuff removed by the water change is equal to the total change between water changes.

So if you do a 1/4 water change, the system build up to 4 times the total change between water changes. 1/10 10 times, 1/20 20 times and so on.

Plus whatever is in the replacement water.

Of course that assumes the stuff is a linear measure unlike things like pH.

And that you have a constant change between water changes also.


So

amount before water change=(amount in replacement water)+(total build up between water changes)/(fraction of water changes)

If you do a spreadsheet on water changes and do a plot, you will find that the system will approach that point.

Also notice this does not matter where the system started at. You could start at any old point and with an infinite number of water changes the end point is the same.

Of course we don't have time to do infinite water changes, but it will be within test kit results after 10-20 or so water changes.

And obviously things don't stay linear forever. For instance, calcium can't decrease at 1ppm/day forever. You run out of calcium. And things like nitrate and phosphate react to algae/coral build ups in the system. and bioload changes and feeding also.

But I make those assumptions to get a handle on how effective water changes are.

any extended agreement with reality may be purely accidental. LOL

 

[beaslbob]

wooopsies.

Got kinda long winded on that one.

Hope it helped anyway.

 

[Faulkner’s maze]

That's a fine reason to use larger and less frequent changes.

Otherwise, I typically prefer and did smaller ones (actually, nearly continuous in my system, with 20 15 minute periods of slow water change each day).

As to the actual effect on the efficiency of the change, I discuss that and show graphs and such in the article linked above.

Def great article. I do like the idea of a 10% additional water change in addition to the daily

Some great input from everyone. Thanks all!