Keep in mind that even the grass and redfins can get over 12" and if your 75 a long instead of a wide (it's 12" wide instead of 18") because these fish are not as flexible as many others, they will have a hard time turning around at maturity in a tank that is as wide or smaller than they are long.
If the 75 is a wide, it will be perfect for a grass or redfin pickerel for life.
Before you get one though, also consider that there are very few tankmates for a pickerel, so be sure you will really like the fish, cause it's most likely all you will see in the tank. Anything smaller and the pickerel will eat it, anything larger, and it will likely bully the pickerel which is a ambush predetor. (They don't move a whole lot when not feeding)
And you will most likely be feeding live all the time, as I have only heard a few remarks of people pellet training theirs.