My corals are out of the water for about 10 minutes or so when I change water,no problem.But as Marie said,if its going to be a while,its better to turn them off,just to be safe.

I agree. If the water has some sort of contamination a small water change is unlikely to lower the concentrations enough to fix the problem. Of course you dont want big temperature or salinity swings but those are easy enough to match up.

Many reefs are close to the surface and experience salinity changes with rain. It doesn't wipe them out.

Personally, I think as long as the water is the same temp and salinity, change as much as you want as long as it's the same bucket of salt. If it's a new bucket, I'd test a few more things, pH and Alk specifically. I would of course suggest that there is some degree of confidence that the water is the issue. I've done up to 90% changes before with no problems other than using most of a bucket of salt. Make sure it's pre-mixed for a day though, or heavily mixed and aerated if required same day.

I agree the pre-mix for 24 hours or so, when doing such a large water change. I couldn't do 50% in a 230g, impossible, but I would have loved to.

My FOWLR has a few softies/LPS and been set up several months now skimmerless. I think the 50% waterchanges make all the difference there.:wink:

I have done 50% water changes many times before & when I upgrade my tanks, I usually use 40-50% of the original water & add new water for the rest. I find my corals loved these massive water changes (as long as salinity & temp. were close). Two weeks ago, I did roughly 120g worth of water changes on my main system & everything is thriving.

Anthony

I never have to drain the main display for waterchanges only the sump, therefore the corals remain in water but I find large water changes good for certain corals ie softies but not too well for sps anyone agree?

I've never had a problem in the past with large water changes and sps. Of course the last 18 months all my sps are in my 175g and I don't have a mixing bucket big enough to do a large water change, I wish I did :lol:

I did a 100% water change once, solved my nitrate buildup pretty lickedy-split :lol: But it was a 20g tank and it had no fish, only a carpet anemone and some corals. But they all liked the outcome ... :)

There are times when I look at my 110g cube tank now with its elevated nitrates and I wish I could do a 100% changeout, I just don't have enough reservoirs to do it (and I have fish in there so that's no good). But I'd love to be able to change out even 50% or 75% of it just to be a kick-in-the-melon to the nitrates that are there.

Other than the bad salt (Kent, about a year ago? Maybe 2 years ago now, when they had that alk issue??), I've never had an issue from the waterchange itself. But yeah, I do match the temp and SG carefully, and do the premix for 24 hours thing too, so that probably helps a bit. I'd hate to see the results of a large scale water change that introduced a drastic temperature change.

I tell you one thing though, and maybe it's worse for me than others since I have tanks that have at least 5 years of crud buildup in the plumbing, when I turn the pumps off and turn them back on, the stuff that comes flying out of the sump return outputs is something I wonder if it would be better off not having been disturbed and released "en masse" into the water (ie, did I just invalidate my water change). I need a way to scrape out the pipes :lol: Or maybe it's better just to redo the plumbing every few years or so :eek:

It's interesting that nobody is speaking up for the small water changes.

It was comments like this

and this

that got me curious.

It's not just canreef but on every reef forum I visit, there is a group of people who will tell you to never change out more then 10-20% of the water. I think that a lot of tank crashes could of been saved over the years if people were more willing to trust the lone person who says "Do a 90% water change" :biggrin:

Marie, I completely agree. While I regularly do 10 or 15% changes for maintenance, if I thought I had an issue that a 100% change would fix, I'd do it ( well, back when I had a 100g tub for mixing). The "rule" of 10% is just being safe and we always tout "make small changes slowly" in a reef, but properly prepared water is just like the water in the tank without all the crud in it.