Doing super frequent water changes.. what can go wrong?
 

I want to try an experiment and was wondering about a couple of things. What i want to do is try to achieve an ULNS by doing very frequent water changes. Like, i'm talking 10% every 2 to 3 days. I have a 150g system so that's 15g every 2 to 3 days. What I'm wondering is what will be the fallout? I suspect the natural fauna of the tank could be diminished, but enough to be a problem? Has anyone ever tried this? Searching through the forums it seems the average minimum is about a week for a water change. My logic is that the natural ocean works well because it is highly diluted. Well, I figure if I inject new saltwater very frequently then I could nearly achieve this. So what's wrong with this logic?

hmm, interesting thought. Well I cant see anything bad about it, concidering when you have a najor nitrate issue, you ussally want to do frequent water changes. And all your doing when doing water changes is taking out old water and adding fresh new water with replenished elements in it. Now i suppose the reason why most people stick to weekly water changes is because its cheaper, yet still making sure that the tank stays healthy at the same time.

I would say try it out, and tell us of the outcome.

Ulns?

Ultra Low Nutrient System

Water Changing
 

I maintained a similar routine with a tank a few years back...

Every 3rd day i changed out 10% for over 6 months. I never did notice much of a difference. The nutrient levels did seem to reduce initialy, but i found that the skimmer would hardly produce any skimate. I suspect this was down to the dilution of waste although the skimmers weren't the best back then. Believe it or not, I did notice the nutrient levels actually increase over the long run! I put that down to the fact that i was using tap water :redface: and not R/O....:neutral: I think i was putting much more of the bad stuff back in :biggrin:

Ended up being a Chore.:sad:

Would be interested to know how you get on.....

Simon..

The biggest fallout is the cost of salt.

It's actually not that new of an idea. I'll have to check back some old threads but there are several articles are written about the idea of water changes and how basically there is a point of diminishing returns with them, and basically, not unlike feeding, "smaller more often" is better than "larger less often". Some systems in fact incorporate constant water changes - ie, there is always a steady stream or drip coming in and it just overflows into the drain. Some captive breeding systems are setup this way. You would have to measure your salinity though regularly and manually compensate for the drift.

To be honest though I'm not real sure you'd get a "true" ULNS out of increased water changes. Your rate of export has to match or exceed your rate of production and since one is steady state and one is stepped, I don't think you will truly get there. I think the tank will certainly benefit, but it's not an as aggressive method of nutrient removal as the bacterial based ULNS's.

I think it really comes down to time, energy and cost. Otherwise it's pretty much just win.

hmm maybe no need for a skimmer anymore mith that many water changes

I did think about the cost and reasoned that the amount of salt that I would need would probably be near what larger systems, say, 280g and up would use on a regular basis anyway? Plus, if this did produce an ULNS then that would eliminate the need for additives, but it sounds like this wouldn't be the case :sad:

.. thinking out loud here.. I wonder what would happen if you did frequent enough water changes to the point where the water in the tank was (nearly) constantly equal to fresh saltwater. Like say 90% fresh saltwater all the time?

well your corals would grow nice and fast and the fish would be healthy thats for sure.

We might be getting into two separate topics though here: reefbuilding and nutrient management. Dosing is really more about managing parameters that are directly responsible for coral growth; nutrient export helps growth in that nutrient buildup will inhibit growth so removing nutrients (and by extension, ULNS) will remove those inhibiting factors. But even a zero nutrient system won't grow corals if there is no calcium or alkalinity or magnesium to begin with.

So. Water changes does benefit both goals by removing the baddies and replacing the goodies that get used up. Certainly there are tanks out there that use only water changes as the primary tool and these are nice setups. And indeed, do enough water changes and you might not really need a skimmer.

But what I think you'll find is that with water changes alone, you will only be able to go so far with it. In a low demand system, it may be enough forever. But in a high demand system (such as one with SPS), the draw on the calcium and alkalinity is not linear over time. Ie., as your corals grow bigger, so too does their apetites for calcium, and thus you have to add more Ca and Alk to compensate. At a point you will find, I think anyhow, that water changes alone won't cut it, and you have to manually replace Ca and Alk anyhow (either by dosing or by calcium reactor). The main thing about this is that the Ca and Alk is now decoupled from the nutrient export - which ultimately is a good thing because the rate of Ca and Alk usage likely isn't directly proportional to the nutrient buildup (which is going to depend on the fish load, and how much/how often you feed, etc.)

So, I'm not saying I think it's a "bad" idea, but I think it's just not the most efficient or cost-effective method out there.