Nitrite / Nitrate / ammonia levels are high

[duanes]

If you had used a couple handfuls of substrate from other tanks, and the suspended spore product,
the new tank would have been instantly cycled.
There is a wait while bottled bacteria spores become established.

In my sump I use 3x 3" bags of biological media (the rest are plants)

Many people think, the more media the better.
But efficiency of biological filtration is not based around volume of media.....its about the food to micro-organism ratio.
More biological media does not promote more bacteria, more beneficial bacteria are the result of their food supply (volume of fish waste) and whether of not the DO is sufficient to maintain that populatiion (aeration and flow thru media).
A sump packed and stuffed with various types of biomedia will not process any more waste, than my 3 three inch bags of rings, because that population (and biofilm) is not about volume, but upon the bacteria food supply.
Of course the plants also support surfaces for beneficial to live on, but their added benefit, is that they also process, and consume nitrate.
Simple bio media produces nitrate as a byproduct of processing amonia and nitrite

 

[danotaylor]

Absolutely agree w duanes explanation.
If you add all those other fish at 1 time you will be increasing your current bioload by well over 1000% and your bio-filter will not cope with the amount of dissolved waste. The result will he a potentially catastrophic increase in ammonia and nitrite which would like kill your fish. You would need to add some substrate and nature media from an existing tank to avoid this crisis.