Moving 29 gal Biocube

[naesco]

IMO you can have perfect salinity, ph, calcium, alk etcetera but by doing a 100 percent water change you are exchanging a mature tank for a sterile tank and IMO that is not a good idea.
You remove all the goodness in the water ie. bacteria, tiny critters, egg hatches etc. that stabilize your water and feed your coral

[asylumdown]

Originally Posted by naesco

IMO you can have perfect salinity, ph, calcium, alk etcetera but by doing a 100 percent water change you are exchanging a mature tank for a sterile tank and IMO that is not a good idea.
You remove all the goodness in the water ie. bacteria, tiny critters, egg hatches etc. that stabilize your water and feed your coral

I'm not saying that's not a possibility, but my main questions out of your statement would be this:

1. are there actually any measurable levels of the things your worried about removing floating around in the water column of an aquarium that's being skimmed (and may also have filter socks in it) at any one moment in time. It's been pretty well established that the important bacteria (ie, the ones that process wastes) are all substrate bound, they're not actually in the water column. If there's a spawning event in your tank, how long do those eggs and sperm actually stay in the water before they're eaten or skimmed out? What you're talking about are substances that are contributed to the water column on an ongoing basis and are routinely removed, not things that are self reproducing and sustaining within the water column itself. Based on how quickly my water returns to crystal clear after I feed, I would guess that the 'half life' of any macro organic substance (eggs, bacteria, critters, etc.) in the water column is going to be vanishingly short, so whatever is in it from moment to moment was most likely contributed relatively recently. The replacement water will likely have the same concentration of eggs, critters, and bacteria as the old water in a matter of hours. I would suspect that relative to the real ocean, the water in our tanks is vastly more sterile in general to begin with, but that doesn't seem to affect the growth of corals.

2. assuming those things are present, does their presence actually matter from a 'captive reef health' point of view, or does the benefit of routinely bringing your dissolved nutrients down to near natural reef levels, and bringing your dissolved trace ion levels that you may not even be testing or dosing back to the 'optimal' levels far outweigh any negative effect that removing a few ephemeral bristleworm eggs might have?

3. What do you mean by 'stabilize'? There are terms that we use in colloquial speech that sound like they mean something, but when you pull back the curtains a little bit, are actually functionally meaningless unless they're specifically defined. The way the alternative health industry talks about 'toxins' in our bodies is one of those cases, and I would argue that in the reef world 'system shock' and 'stabilize' are another. Stabilize in what sense? Keep ammonia levels at a constantly undetectable level? Keep calcium levels high? Keep dissolved nutrients low over time? "Stabilize" can mean a lot of things, and when you think about the functional and tangible parameters that you're actually talking about when you use words like 'stability' and 'shock', 100% water changes do not necessarily trigger changes in those parameters that are actually harmful to tank inhabitants in any way.

I would argue that you don't even need to perfectly match calcium, alk, etc. when you do a 100% water change, as the range of those parameters that marine organisms seem to be able to thrive in is wide enough that the degree of difference necessary to cause real, cellular 'shock' for most things will be wider than a properly done 100% water change with high quality reef salt will ever cause. Salinity and temperature are something that cells have a hard time adjusting to when it's changed suddenly (though I would argue that temperature has a much wider range of allowable sudden changes than most people would be comfortable experimenting with), which is why 100% water changes are always recommended to match exactly.

[asylumdown]

I should also mention that sudden changes in pH is another one of the things that can probably cause damage. But I would also argue that if your discarded water has a pH that has gotten high or low enough for the sudden differential a 100% water change will result in to cause cellular damage, you've got far more serious, longer term water chemistry problems, and a a 100% water change is probably an advisable short term risk to get your system out of a dangerous zone.

[asylumdown]

ugh, three posts in a row. Put the soap box away adam.

The last thing I'd say about the real risk to 100% water changes (assuming that it's your only method of maintaining a tank) is not that it can take something like dKH from 6 to 8, it's that between the water changes, your dKH is allowed to fall from 6 to 8. It's the ongoing, day to day stability that matters, and if over a week your levels are fluctuating from very low to very high, or very high to very low and you're doing nothing in between to keep them 'stabile', you're either not doing your 100% water changes regularly enough, or you're not doing enough in between the water changes to keep things stable.