Dave, I don't know how big your system is, but if your fish sat in the tank long enough to completely rot then I would change all of the water. Do you have live rock. Did your invertebrate life eat the dead fish, or did your brother take them out fairly soon. This all has an effect on the water. If the fish rotted then change lots, if they got eaten or removed then its not such a big deal. I would still do a decent water change but it won't be so bad. My tank is really big and I use R O water. [compete tank meltdown using tap water when i just started]. Unless the fish is one of my bigger ones, it would get eaten before I realized it was dead. If this was my system, I would do a moderate water change. Put your new skimmer and filter on and let it run. Break in the skimmer and filter, for a couple of wks, Do a water change every wk. After a couple wks, and a couple water changes, if your skimmer is doing its job, then start with restocking. Don"t be in a hurry and don't start with $$fish. It really hurts when you lose one you paid 2 or 3 hundred for, specially when its your own stupidity that kills it.
I don't recomend this way but this is how i do mine and it works for me.- syphon hose 6 to 8 five gal buckets out. However much i am taking out i have on hand with ro water. because the 5 gal buckets are so heavy when full and i have to lift them up to 5 ft, i dump 2.5 gal in fresh in the bucket then right in the tank. i mix the salt with the other 2.5 gal, let it sit for 10-20 min stirring ocassionaly, then in it goes. continue till proper amount of water and salt goes in. i don't adjust for temp either. i would not do this with a small tank though. mine is 265 gal. with a lot of curculation . usually only drops by one degree.i have never had anything shock or close up, but i am careful to never dump on top of anything. and yes i can hear all the gasps of shock With water change cleaning filter pump and skimmer and sucking any thing of the bottom i want to remove maybe an hr.
