The sump won't fit all the rock from the 90, but I'll put 40 or 50 pounds in. The trasfer might take a while as I'm cutting all the corals off the existing rock and remounting to the new rock. So I have to at least keep the 90 3/4 full and just use the water from the sump.

Yeah you should be fine if you can use as much water and rock as possible from the 90. The rock is obviously more important since the water actually has little bacteria in comparison. Is there any reason why you can't use more rock from the 90 and less from the bath tub? Also maybe you can move some of the corals with the attached rock to speed things up and then as time goes on you can do a little rearranging in the 180 when things are 100% stable.
The faster the better IMO and I would spend your time and focus on the 180 rather than trying to maintain the 90 as well.

If it helps pretend your 90 gallon is going to explode in a the next few days and you're not sure exactly when, could be tomorrow or next week. Better work fast! :wink:

lol, ya, I'm going the exploding 90 route, but I want to build all new structures from the new rock. I suppose I could add some of the existing rock around the bottom, but 50 pounds in the sump should be enough, I think. Coupled with the new rock (about 130 pounds), I should be OK bacteria-wise...I think :)

I used prodibio when I swapped tanks , I used stability for the move and strat up throughout the next week or so never had any issues done it all in a few hours.

Consider moving some of the sand as well if you can do it without making too big of a mess. Tons of bacteria there.

Current tank is BB :)

I've upgraded a couple of times and frankly as long as you're not adding uncured rock you're good to go. All you're doing is increasing water volume so unless you're adding a crapload of new livestock to the new tank at the same time as you move the contents of the 90 into the bigger tank you're certainly not increasing the bioload. Even if the rock you have in tubs was dead you're still fine as you're just moving the same bioload from the 90 into a tank with more water. Its like doing a massive waterchange and everyone will be the happier for it (noting temp and salinity is the same of course).

edit: LOL, ok I just missed all of page 2 and basically repeated what sphelps said.

Carry on.... :razz:

If not already mentioned, watch pH closely...turning the skimmer off like that can cause pH to drop quickly enough to cause trouble. If that happens just add a big airstone.

Christy, I'm not moving all of the 90 contents in, and in fact wasn't moving much other than 2 rocks with lots of corals growing on it. But, I can add a fair bit to the new sump, just not all. The rock I'm using should be able to catch up quickly, it's been cooking with food source for over a month.

Mindy, yes, O2 content will be something to watch with the skimmer offline...

Progress report. 180 full, salt added, the sump is setup with my skimmer, the sump for the 90 got shut down last night. I've added some rock to the new setup (in sump). Waiting for temp to come up.

Meanwhile, back in the 90 (without sump or skimmer), my 3 clams decided this afternoon was a good time to spawn. Currently, I can't see the fish....big sigh, didn't see that one coming. Setting up for a water change now, and going to the expidited move schedule, hopefully starting tomorrow..