After your tank is fully cycled then you can start to add a small portion of the total CUC you want. If you add the whole CUC at once you will run into the risk of having some die off due to starvation.
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After you do your cycle and then do about a 33% PWC. Your tank will full of nitrates after the cycle and you`ll need to get rid of as much as you can with a big PWC and then frequent one after that.