I completely agree, stability is key for long term health. But when there is plenty of practical evidence showing that very large to 100% water changes harm nothing and can allow systems to maintain stocking, feeding, and dosing regiments that wouldn't otherwise be possible and still have award worthy coral growth and healthy fish, I think that should be pointed out, especially when someone is new to the hobby and is worried about moving a tank.

Anyway this is all testable. I'm doing a 100% water change on my pico in about 5 minutes. Both the bag of ceramic bio-rings in the back chamber, the rock pyre, and all the corals will be completely exposed to air for about 5 minutes. I'll do that water change, then target feed each one of my corals with meaty foods, which is about the maximum organic input this tank ever receives. I normally wait a couple of days to feed them to get the most out of my low N and P change water and discourage algae, but for this experiment I'll feed them as soon as they re-inflate. I'll test ammonia levels every day for the next week. If I get a detectable reading, I will post it in that tank's build thread. If not, I'm going to continue to operate under the assumption that any 'threat' posed by large to 100% water changes (when done right) is largely superstition.

+1. I change 90% of my water in my picos. Have had no ill effects. No losses to date. Water changes are the life-blood of this fascinating hobby. IMO.

Can you please post a reference for your claim? As far as I know, if the salinity doesn't drop below 1.018 or its not left to dry in the sun, the bacteria don't have any effect. I don't see people "drip acclimating" LR before adding to the system.

I actually didn't see that line until right now. I should clarify, the two cases in which I've seen people using 50-100% water changes on large systems were using actual sea water, pulled from the ocean using a pump. They both live basically on the ocean in Australia, so this is possible for them, and the only thing they need to worry about it keeping the water the right temp. However, in the case of the 95% water change system, it's an SPS LOADED tank, and I don't think he doses anything (thought I can't confirm that anywhere that I've seen), so his alk, mag, and calcium levels are going to be quite depleted by the time he does the replacement. The guy who's doing 50% weekly water changes is dosing something to maintain alkalinity, but as far as I know that's it. I would happily do 100% water changes on my big system using high quality salt , but I have neither the logistical capacity, or the money to sustain that in Calgary.

I'm running a little experiment with my pico now if you want to look at it. I tested all the levels and the ammonia right before and after a 100% water change yesterday, then fed the corals in that tank about 25% more food than that tank ever usually gets in a single feeding. I tested the ammonia again today, and will test every day for the next week. I will also feed again around Wednesday. If I've done something to the capacity of the bacteria in the tank to process waste, I should see a spike in ammonia in the tank.

is this the guy you were referring to by any chance?http://www.youtube.com/watch?feature...&v=Y5tVuqYFf48[

QUOTE=asylumdown;829142]I actually didn't see that line until right now. I should clarify, the two cases in which I've seen people using 50-100% water changes on large systems were using actual sea water, pulled from the ocean using a pump. They both live basically on the ocean in Australia, so this is possible for them, and the only thing they need to worry about it keeping the water the right temp. However, in the case of the 95% water change system, it's an SPS LOADED tank, and I don't think he doses anything (thought I can't confirm that anywhere that I've seen), so his alk, mag, and calcium levels are going to be quite depleted by the time he does the replacement. The guy who's doing 50% weekly water changes is dosing something to maintain alkalinity, but as far as I know that's it. I would happily do 100% water changes on my big system using high quality salt , but I have neither the logistical capacity, or the money to sustain that in Calgary.

I'm running a little experiment with my pico now if you want to look at it. I tested all the levels and the ammonia right before and after a 100% water change yesterday, then fed the corals in that tank about 25% more food than that tank ever usually gets in a single feeding. I tested the ammonia again today, and will test every day for the next week. I will also feed again around Wednesday. If I've done something to the capacity of the bacteria in the tank to process waste, I should see a spike in ammonia in the tank.[/quote]

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

yah that guy! I haven't watched the full video in a long time, does he give more specifics on what he does between water changes?

i've seen this vid last year and was reminded about him while reading this thread..:wink:

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.

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.