confused and concerned

[greengills]

anyone that may have an idea of what i am doing wrong- please help me out
here is what i have:
75 gal bow fish only
1 year running
nh3-0
no2-.03
ph-7.5
no3-22.5
salt-1.020
temp-80
kh-4.0
balloon puffer,neon puffer,striped goat,chain moray,orange spot blennie.
the problem- certain fish, when i introduce them to the tank, die within a week while showing no signs of sickness before hand-happens over a 2-3 day period. this is confusing because the fish i have now, i have had over 3-4 months, and a couple from when i cycled the tank for the first time.
whas the deal? there are some nice additions that i would like to make, but can't play roulette with their lives!
any advice would be followed and appreciated!
thanks all.

 

[seatank]

ok this is what i think
no2 should be 0
ph should be a min of 8.0 max 8.5
salt should be at 1.023
temp is ok but try to bring it down to about 76-80 i keep mine at 78 degrees.
SHARKS!! please correct me if i am wrong.

 

[goofieones]

For a fish only, a temp of 80 is fine, the salt at 1.020 is fine. But PH too low, strive for 8.2, but should maintain at least 8.0. You can buy some PH stuff that will raise the PH to 8.2. And of cours amonia should be 0 along with nitrites 0, but nitrates are okay below 60.

 

[jimi]

Here is my opinion ammonia and nitites need to be 0. Nitrates below 30 its not ok to be 60 as someone said. Salinity 1.023, temp 77,and ph definately above 8.0 but another guess would be your puffers release small amounts of toxins that your fish have become immune to.