help, some fish die some don't

[aj565]

to start with here is my water conditions.
75g tank 20g fuge
30 Nitrate
0 Nitrite
200 Alkalinity
8.1 PH
1.023
i have 52 lbs of live rock and 80 lbs of live sand a fuge and a skimmer.
the fish i have in the tank right now are 3 scissor tails and 4 chromis.
i also have 10 astrea snails 4 nassarius snails and maybe 10-15 zebra and scarlet crabs. the tank has been running for about 2 1/2 months and cycled in about 3 weeks, i used about 10 gallons of Natural Sea Water. i added fish in this order, 2 chromis about 2 weeks after cycle ended, 2 more chromis 1 week later, 3 scissor tails 1 1/2 weeks later, bicolor blenny 1 week later, 3 firefish 2 weeks later and the two spot blenny a week after that.
my problem is i had 3 firefish and a two spot goby and 1 bicolor blenny. everyone was eating and all was well. and now the two spot was hiding and i only saw him once after a few days and never again. the firefish went into hiding and i could see them in the rock but they never came out and one of there bodies has since come out. and just yesterday i lost the bicolor into the rock somewhere. the chromis and sissor tails are still out and doing just great but everything else ends up hiding/dieing. it seemed everything was doing good for a few weeks then went into hiding and then dead and i have no idea whats going on, anyone have an idea what to look for? i check the water about once a day to make sure something doesn't spike again. i'm just kind of baffled by why i'm only loosing those fish and not the others.

 

[mie]

some fish are hardier than others sorry about your loss

what is your ammonia level, and temp? did you increse or decrease your salinity or temp in a hurry by any means i.e water change with low salinity ?????

 

[aj565]

ammonia is less than .25 and the temp is 78*. I do water changes with Nutri-SeaWater since i don't want to mess with mixing water and i top off with RO from my LFS or wal-mart. the fish were fine and the bicolor was doing great for a month or so and then just started to act funny about 2 days ago and was gone this morning. i should add that i had 2 dimond gobys and both jumped out and both times the tank was covered the first one got out threw a 1/2 hole by my drain back pipe and the other jumped threw egg crate i'm kinda wondering if there is something messing with them at night. all the fish lost so far are on the left side of my tank near the bottom of the rock work and the fish i still have stay near the top back of the right side rock work. :help:

 

[mie]

How strange you might have a hidden aggresor in there or it is posible that your fish are recieving a shock from your heater which could be faulty this might explain why they would jump out and or dying. this is just a possiblity that i have heard about

 

[rbaldino]

If your scissortails are gobies, they're probably picking off the firefish, and maybe the blennies too. Some fish, when put together in a small space like an aquarium, will become aggressive towards similar or identical species because they feel a need to be more competitive in an environment with limited resources. They basically feel threatened by fish that are like them because they know they're going to be going after the same things, like caves, food, etc. It's unlikely that some hidden predator is taking them out; the aggression seems to be limited to very particular fish, yet they're all equally vulnerable.

 

[aj565]

Originally Posted by rbaldino
If your scissortails are gobies, they're probably picking off the firefish, and maybe the blennies too. Some fish, when put together in a small space like an aquarium, will become aggressive towards similar or identical species because they feel a need to be more competitive in an environment with limited resources. They basically feel threatened by fish that are like them because they know they're going to be going after the same things, like caves, food, etc. It's unlikely that some hidden predator is taking them out; the aggression seems to be limited to very particular fish, yet they're all equally vulnerable.
see i asked 3 different LFS before i bought the firefish and the bicolor blenny if the scissortail gobies would pick on them since they looked alot alike and they all said no. i know about the stories about LFS but 1 i really trust because he has never told me wrong and what he says is the same things i read on here. another deals in saltwater only so i figured they would know. if this is the problem then it answers all my questions but 1 and thats the two spot gobie since they look nothing like a scissortail. maybe i'll trade the 3 of them in so i don't have to worrie about it anymore.
doubt its the heater plus its in the fuge.

 

[mie]

Just a thought