What are tape credits, their amounts and who gets them and why? If it's the broker who keeps it should it not be the trader who generates them share in them as well.
Where the heck did you get the term "tape credits"? I assume you actually mean ECN rebates/fees. If you want ECN rebates then use a broker that has an unbundled commission structure and pays ECN rebates and charges ECN fees. For a detailed list of ECN rebates/fees look at http://www.interactivebrokers.com/en/accounts/fees/commission.php?ib_entity=llc
I am not referring to ecn credits/debits. Tape credits are mentioned in the fee schedule of the Nasdaq and all other ecn's. It mentions a 50% credit. It looks like just for posting a bid/offer that is filled it generates some kind of credit to the broker.