Dyeing fish

Question
Happy Holidays.  I have a self made terrarium (85? gallons) with land on both sides and an island.  We live in Hawaii and put anything we catch in the tank.  I have 3 crabs, numerous hermit crabs, snails, blennies, a sea urchin, sea cucumber, 3 feather dusters (store bought), 2 juvenile flagtails (Kuhlia xenura), tidepool gobies,a clown fish (store bought), a surfperch(?)  and some unknown minnows and fish.  Recently we caught two saddle wrasses and a tang.  They died within 2 days.  All Parameters were good but the Nitrate level was very high (70).  I went to the ocean and hauled up enough water to change 2/3 of the water.  That was a week ago.  Since then I've added the feather dusters and three jumbo shrimp (bought from a shrimp shop on the north shore.  After I changed the water and added the shrimp some creatures began to die.  (1 flag tail, 1 gobie/ blennie, all three feather dusters, the clownfish, the sea urchin, 1 shrimp)  All the other fish looked sluggish.   I checked the salinity and it was high (37.)  I took out a little saltwater and added freshwater and the salinity went down to 34.  I checked the Nitrate and it was still high (20.  I would like to make my terrarium healthy enough to put reef fish we catch in it but I don't want to kill any.  What can I do?
Thanks,
Ben

Answer
hey Ben,

Where in hawaii do you live??  I grew up in Haleiwa...

Im not real clear on your setup... Can you explain it a little bit more for me???  Im not sure how you get flow/circulation... it is uber important that water flow, all the time, and all over the tank...

Water motion will circulate the water around the rocks and sand, or maybe it is better to say through the rock and sand...

it is the biological organisms in the rock and sand that grow and digest the ammonia and covert it into nitrates...

It is also important for the fish to have some surge action.

Salinity is not that difficult to dial in, but it needs a constant addition of fresh water as salt water does not evaporate, only the fresh water, so you will need to add fresh water all the time, once you get your salinity to where you want it.. 35ppm/1.026

Once you get it to that level, make a mark on the tank, and when water levels draop, just add fresh water, (filtered / ro-di water)

Please contact me on my new forum at www.thelittleocean.com

we can talk / discuss this better over there as they have better editors and more folks to help offer tips...

I would also love to talk with you about my old home, and have actually been contemplating a return move back there now that my daughter has moved out....but know now is not the time to be looking for homes on the north shore...:)


anyways, i look forward to hearing more about your system soon.


bill