water change question

[randolph]

my nitrates are high and planning a 50% water change
how much can i bring them down with a change that large, or should i do 25% about 3 times over a week or so
ammo-0
nitritres-0
nitrates around 50 maybe
had a green chromis die and thought it would be good food for starfish and crabs, probably not a good idea?
green button closed up so i mixed some fresh saltwater put him in a tupperware bowl and currently floating in tank good move or not?
thanks for any help
been at this for 22 months and have had real good luck till now
brought home an flame angel and he had or developed ick been down hill since. just added new lights and tank is really looking great, went from 2-15 watt 50/50 to 1-96 10k white, 1-96 watt blue
need to get it back on track

 

[aqua blue]

With your tank being up for 22 months the biological filtering is probably well established and therefore converted the ammonia caused by the dead fish to be converted to nitrites and then to nitrates at a quicker rate.
From what I have read on this bb if you want to reduce bad levels in you water conditions by 50% then you would need to do a water change of 50%.
Others with more knowledge will probably give better info. This bb is a goldmine for helpful knowledge.
Good Luck

 

[fshhub]

i would remove teh corpse, it could create a spike, if not eaten, and spikes are not a good thing with inverts esp real sensative ones like starfish