So my cycle seems to have stalled at high nitrates. Help please? :D

[Myka]

I don't know anything about a non-circulating biopellet reactor, sorry. The IO product seems like a good choice for a nano tank or an application where there is no space for a reactor. Overdosing would be the same as biopellets (or any other carbon source) where the biggest problem would be bacteria bloom which threatens the tank with oxygen deprivation (lethal firstly to fish). So essentially not usually a problem with a functioning skimmer.