i had to do it and it sucked real bad, i moved all the inverts and asmuch live rock that i could and in a 130g tank it took a while to drop the sg
low enough wich was a huge pain then i had major die off so amonia went through the roof and i was doing 30g water changes every day for almost 2 weeks and i still got a big time bacterial infection in the fish(ich was gone though) wich killed a 3 striped damsil a 10" lion and a 8" cowfish the yellow tang and the domino damsil got big sores but lived the snowflake eel showed no signs of anything, so after about 8 weeks raising the sg
back up cost me 2 buckets of salt and another 200g of water changing time and right when everythig got back to normal the tang and domino were showing signs of hlle
wich both are doing fine now and are on a high vitamin diet.
i downsized the 130 to a 67g wich i use for a qt
tank the eel went into a nother 130g i have about 2-3 monthes latter i adopted a grouper and fox face and got ich again i went the copper route and had a small die off wich a couple waterchanges keept under control the ich dissapered shortly after and had no other problems so as you could probably guess i dont hypo anymore.