Fragmaster et. al., Please forgive the extended ramblings below...they're "out loud thought" and posted simply to foster discussion, consideration, and perhaps some different thinking.
By no means am I trying a no-water-change in 14 years kinda setup with either of our reefs...that's another challenge for another tank, and was simply used as an "exteme" example to illustrate my point.
In theory, a 0 water change tank IS possible. It's not like salt or H20 go bad....
Think of it this way. We mix up saltwater with a chemically formulated salt mix. In theory, it's good to go, and if it was sealed and sterile, it would never change.
But instead, we put it in a glass box, put living creatures of all sorts in it. These creatures use up resources and create waste, but if we never input anything past this point, our "glass box" would rather quickly "crash".
We're not out of the woods yet...we have to feed them..introducing a mixture of organic and inorganic compounds that provide nurishment. As a result, waste is created. If this waste builds up, it can poison the inhabitants of our aquarium and alter the chemistry of the initial saltwater mix making it unsuitable for the creatures existing in it.
So we add filtration, to help maintain better conditions for our living creatures. We promote gas exchange with the air around us to help maintain proper levels of gases IN the water. Our filtration helps remove toxins and break down waste into more benign forms, but even so, if this "less toxic" waste ultimately builds up and needs to be dealt with.
ONLY AT THIS POINT did we as aquarists discover the power of a "water change", which dilutes the waste and replaces a portion of our "less suitable" water with "better" water. Or maybe, and more historically accurate, ONLY at this point did we LESSEN our dependency on the "water change" to maintain a healthy watery environment. Afterall, I assume most all of us had a goldfish bowl at some point in our youths. Water changes is all it took...but you had to do them all the freakin' time.
We've come a long way since that POINT. Through hobbyist trial and error as well as scientific examination, we know a LOT more about what happens in our "glass boxes".
So back to that initial "freshly mixed up saltwater". 70 or so various components plus "trace elements", besides H20, which pretty much match everything we know about the natural water chemistry of the ocean. We lose H20 by evaporation but return it with top offs. We input "energy" as food & light. Waste builds up but can be UTILIZED by other organisms as a nutrition for growth. These organisms may use other elements from the water as building blocks and we replace them, just like evaporated H20.
In theory, if we balance the closed system properly, why would we need water changes? BALANCE is the key word.
Let's briefly examine all the arguments "for" why we aquarists NEED and RELY UPON water changes.
1. Dilute Waste (nitrogen) - easily handled by denitrifying bacteria, marine algaes, corals, "nutient export" (i.e. harvest and disposal of macro algaes)
2. Replacing elements as they are "used up" - well, could be handled by simply adding them back IN.
#3? In reality, what other reasons DO people do water changes? There really is no #3 I can think of.
We either perform water changes as a profolactic measure to handle #1 and #2 and keep them in check, OR we do them to QUICKLY RESTORE "ideal" parameters in the aquarium when things go awry via the dilution effect. If we're confident that waste and essential elements are OK, and growth, behavior and health are OK, WHY DO A WATER CHANGE?
We can all agree that the creatures we keep in our homes DO NOT like change....they come from an extremely stable environment (the ocean). When's the last time you did a water change of "reasonable size" (i.e. 10-25% as so many of us do) and the organisms in the tank DID NOT "react" with closed polyps etc...
To bring this off-topic diatribe full circle, I have no doubts that the aquarium I cited earlier as having gone 14 years without a water change IS a legimate claim...I have no reason not to believe it. GRANTED, the tank itself has gone through a variety of changes over the years; currently mostly hardier organisms are living in there. Sure, maybe it's not chalk full of SPS or clams or whatever, but it's a healthy reef that has reached a balance point with whatever feeding and dosing is done. It's also a larger (hence more stable) tank...nothing like a 25 gallon cube!
Let's think about it in the simplest terms...why change WATER when there's nothing wrong with the water, ONLY with what's dissolved IN the water? This isn't a "magic pill" type situation, but some common sense has to play a role. Organic waste can be handled through a variety of means other than water changes. "Nutrient/Trace Element/"Building Block"" type depleations can be handled with adding what's depleted, without having to remove and replace the perfectly good H20 in the process.
So when all testable levels are in order, I'm hesitant to do a water change...typically I have to start back dosing right away to bring things like Calcium back where I want them! WHY would I want to go through that when there's NOTHING wrong with the water in the tank based on all my tests and observations of behaviors and general health?!?
When things get out of order, i.e. the clam deaths, I did a fairly sizeable water change because things DID end up "out of whack". But once they're in line, or at least manageable without a water change, I'm not going to add on the stress of a water change.
Think of my chosen route (to avoid water changes) as "bed rest" for the clams. Additional, frequent (daily?) water changes on our clam tank would have been like sending a person with the flu to stand out in the cold for an hour each day, along with all the HEALTHY people who also live in the house.
I've personally ruled out most every explanation for this wipe-out except one. NOTHING in the tank has been affected negatively through this entire time EXCEPT for bivalves molluscs (clams), and even then, somehow 3 seem to still be OK. Accute environmental problems would have manifested themselves in a corresponding accute timeframe. General or ongoing environmental problems (i.e. slow bioaccumulated poisoning) would have progressed along a timeline corresponding to the length of exposure for each individual specimen...as it would take a set time to reach a fatal level. BOTH of these "environmental" situations by all accounts and experiences SHOULD have affected other life in the tank in ADDITION to the clams, and yet ALL OTHER LIFE (and a couple clams) are totally unafflicted and are HEALTHY, GROWING and whenever possible, REPRODUCING. There's only one situation that fits the profile of only afflicting a particular population within the overall population, attacking both new and old residents, killing in a short time frame (hours to a couple days), but only taking down one or two of the individuals in the population at a time. It all adds up to DISEASE. As we pretty much have NO good method for TREATING invertebrate diseases (heck, seems like we really don't even know much about what they are to begin with), it make sense that a "high density" population could crash so quickly, with me being powerless to do anything about it.
So, the iron dosing, well I may pick it up again in a week or two if the remaining clam sticks around...if he lives through a month of it I'll be able to narrow it down (in my mind) to disease as the 100% certain source of of our clam collapse. UV is likely being added to this tank as our only real profolactic for disease in inverts. I'd love to institute a quarantine as we all know that WORKS, but the truth is we just don't have the room.
FWIW,
Matt P.
