I've been dabbling in the hobby for a few years now, currently a 210 gal (250 total vol) DT; mixed reef, fish, live rock, etc. And like any good reefer, I work hard to make my tank thrive.
But this just crossed my mind; if all of my water parameters are stable, what is the sense in doing water changes? I've pretty much spent every other Sunday for the last 3 years doing water changes, but almost think I'm wasting both time & money. If my nitrates are >5 ppm, phosphates >.25 ppm, the nutrients must be in check. And if the Ph, Mg, Cal, Dkh, etc are all within the desired ranges (with assistance from additives), it would seem that the aquarium water is stable and sustainable. So hasn't the introduction of these additives, along with proper filtration kinda replaced the need for regular water changes? I'm eager to hear any and all opinions.
You're absolutely correct in that with a tank balanced out and stabilized, there is no need for water changes. In fact water changes in that case can only cause problems. I for one am not capable of doing anything 100 times without making some kind of error. LOL
Here is my analysis of the effects of water changes. Consider that 1) something is increasing (or decreasing) at some rate call this "rate of change". 2) the replacement water has some of that things in it call that "replacement water stuff". 3) water changes are done at some constant interval called "interval". 4) and finally some fraction of the water is change called "fraction of change". 5) that thing is a linear measure. 6) and sufficient water changes have been done so that the value before the water changes is the same water change to water change. called value before water change.
For instance:
rate of change = 1ppm/day
replacement water =30ppm
interval=10 days
fraction of water change=1/10
In order for the before water change value to be constant, the amount of stuff removed by the water change must equal the build up between changes.
in the above example the build up= 1ppm/day*10 days=10ppm
Removing 1/10 of that must equal to 10ppm build up. so the tank must build up to 100ppm. then drop down to 90ppm and back up t 100ppm for the next water change.
Additionally the 30ppm in the replacement water with infinite water changes would result in 30ppm in the system
So generally:
So the value before water changes=(rate of change)(interval)/(fraction of change)+ replacement water stuff
In the example:
value before water changes=(1ppm/day)*10days)/(1/10)+30ppm
value before water changes=10ppm(/1/10)+30ppm
value before water changes=100ppm+30ppm=130ppm
After water change 120ppm
next water change 130ppm
with 0 ppm in replacement water it's 100ppm to 90ppm back up to 100ppm
Now if you let the headache subside and do a little thinking:
The driving factor is not the 30ppm in the replacement water but rather the 1ppm/day change.
So to me what is important is to get that rate of change as close to 0 as possible. IMHO that is easily done with macro algae consuming the nitrates plus the algae and bacteria consuming the ammonia. With calcium. alk, magnesium you have to dose. Relying on water changes will never result in constant values.
Also frequent smaller water changes will not reduce where the tank winds up. If you consider the interval as say 1%/day you would will see that the above does still apply for a 10% change every 10 days. But a 1% change every day still results in 100ppm before the changes. But the drop is only down to 129ppm then back up to 130ppm the next day. So more frequent smaller changes do result in less drops after the change but the same amount before the water change.
That being said you could maintain the tank with water changes alone. But just not at values that are realizable to the home hobbiest. You could live near the ocean and constantly pump sea water to your house such that your tank is receiving many water changes per day. Most of us can't do that plus the tank is now completely dependent on the replacement water. Whereas balancing the tank out makes it independent of the water used. It could start out a 0, 100, 500, 1000,1,000,000 or whatever. it still winds up at 100 plus whatever is in the replacement water which hopefully also is not a 1,000,000 LOL. So any potable water is sufficient for nitrates. For delicate corals things like copper can still be a problem from what I hear.
So I just start the tank with macro algaes, dose diy 2 part for calc, alk magnesium, and do no water changes. tanks have ran for 5-6 years that way with a heavy fish load and easy type corals.
still it just my long winded .02
