lowering nitrite

Question
I have a 75 gallon freshwater tank with four adult silver dollars, four adult angels, one adult redtail shark, two adult clown loach and a large adult algae eater.  Yesterday morning I awakened to find the algae eater dead and all other fish at water surface gasping for air (very high nitrite!)  I also found an insect in the tank (thousand legs--common name) and I'm assuming the algae eater may have been poisoned.  I'm also assuming his death caused the water to go off the charts.  I removed the dead, did a 50 % water change and removed the silvers and shark to another tank temporarily.  I also added 70 tsp.  aquarium salt.  What else can I do?  Can I put the other fish back in the tank?  I'm concerned about losing everything!

Answer
Dear Paula,
The presence of nitrites must mean your aquarium is still cycling, and has yet to establish enough beneficial bacteria for your current fish bioload.

If your aquarium is still cycling I would leave maybe the silver dollars in the aquarium to finish the cycling and be prepared to change 50% of the aquarium water at the first sign of trouble of high nitrite. With time your bacterial colonies should establish and handle the nitrite problems and you'll be able to add your other fish back in.
An established aquarium should have water parameters as follows- Ammonia-0 Nitrite-0 nitrate 20 or less.

If, however your aquarium has been cycled and established and nitrite has suddenly spiked, I would suspect some kind of depletion of the bacterial colonies or like you mentioned the algae eater's unfortunate death could have caused the sudden spike. Water changes are the best resolvement to this problem above all.

((Clown loaches may be sensitive to salt. Because they are scaleless fish. I wouldn't add them back to an aquarium with so much salt as it may do some serious harm to them))sorry)

You might be best off changing 50% every day until your water levels stablilize and all is well again.

Well, I really hope this helps!!
Only my very best wishes and Best of luck!
Karen~