fair enough :)

Think of it like this..if you bought a fish or coral, and the water was pretty close to your tank, would you acclimate or just add to the tank? Personally, if I get a fish from a friend's tank and we're anywhere near close to temp (that's all I'd look at), I dump the fish in my tank. That effectively is a 100% water change for that fish. I've never lost one to new water. Same with corals. I float a bit to equalize temp, then in it goes. Completely different water than it came from = 100% water change.
The bacteria you want to filter your tank resides on the substrate. The amount free floating will have no impact, so that's not an issue.

I suppose one caveat might be that if your tank is so filthy and the fish have become accustomed to living in sewage, too much of a good thing might kill it. I doubt this is the case :)

I do 50% WC all the time. Though not cost effective I enjoy doing it for fun. Ans as for coral above water I wouldn't worry. Most of mine are exposed and if I'm making frags they sit on table for 5 minutes

I have done as close to 100% water change as you can get (if you don't count the water still trapped in the rocks) with no issues.
If my nitrates were that high I would change out as much water as I could

for those of you who have done such large water changes - what method do you use to pull the water out of the aquarium? and replace it?

a pump seems to be the best idea for something that you would probably want to get done fast rather than relying on siphons

Thanks for all the input

I've had to drain my tank twice to catch fish. I used a large 2.5" hose to drain it into 4 50g drums. I then used a MAG 12 to refill the tank. Takes about 15 minutes total.

I used to have very high nitrates (around 100 ppm). Did many frequent large water changes, and while they would bring the nitrates down a little temporarily, they would climb right back up in time for the next water change (2 weeks). I think my rocks and sand was super saturated with nitrate, and they would just leach out again.

Interestingly, the fish didn't seem to mind, and even my soft and some LPS corals were doing fine. But I did have a major algae problem, and had to clean the rocks and sand constantly.

Tried a few other things too, like a refugium full of chaeto, but that had no effect at all.

Finally used MB7 and got a bio-pellet reactor and that worked, although it took quite a few months. Now my tank has zero nitrates and near zero phosphates, and now have SPS growing well.

The high nitrates could be caused by the media in your canister filter, if you don't need the canister filter I would remove it or at least clean it out once a week.

Way back when I started I did remove 80% of the water and then filled it half way up then back down leaving about 20% then filling up again, but with in a week it was right back where it was.......so I would find the cause and try to reduce that source.