Fish Die But Invertabrates Thrive

[Blinky]

I agree, slowly raise your SG to between 1.024-1.026. Keeping it at 1.021 won't really discourage parasites, to do that you'd need to take it down to levels that will kill your inverts. Lower SG is fine in FO tanks, but with inverts it's best to keep levels as close to NSW levels as possible IMHO.
Right now I'd ditch the condy and then let the tank settle until NH3 and NO2 are 0. Then look into some smaller fish that will live happily in a nano. Unfortunately tangs are out, but there are many other gorgeous fish that will do well in a 30g: many gobies, clownfish, some dwarf angels, some wrasses, damsels, and more.

 

[Pufferpoison]

well Nitrate can be at zero with a cycled tank

I'll explain. I've been having readings as follows: and yes my tank is cycled

Ammonia 0ppm
Nitrite 0ppm
Nitrate 20ppm
Phosphate <.25ppm
copper 0ppm
Alk 11dkh (196.9)
PH 8.2
Calcium roughly 375ppm

ok i've been having hair algae attacks pretty badly. Did some reading and found out I need some Macro Algae (good stuff) like Chaetomorpha which is a spaghetti like algae that is good and uses up the nutrients that the bad stuff uses, but uses it first and basically starves out the bad algaes. So i tested just now (4 days after Chaetomorpha and after i dosed with Kalkwasser and Vinegar) and here's the results:

Ammonia 0ppm
Nitrite 0ppm
Nitrate 0ppm :bday:
phosphate 0ppm :bday:
copper 0ppm
alk 10dkh
ph 8.2
Calcium the same

but i'm working on calcium (starting to use RC instead of IO) so yes you can have 0 Nitrates in a system.