i have two 1500LPH pumps and they are fine no dead spots. xenia can take over the tank
you can add more flow but your fishes and corals may get blasted around the tank. you may just need to buy 2 1500LPH pumps and get rid of the 3000LPH one, because with 2 powerheads you can even out the flow more. it just depends on what corals you are going to have if you are having sps corals you will need more flow. but soft corals dont need that much. im going to add some xenia to my tank some time next month.
some peoples xenia can grow twice the size in one month with low/med flow 
you can add more flow but your fishes and corals may get blasted around the tank. you may just need to buy 2 1500LPH pumps and get rid of the 3000LPH one, because with 2 powerheads you can even out the flow more. it just depends on what corals you are going to have if you are having sps corals you will need more flow. but soft corals dont need that much. im going to add some xenia to my tank some time next month.
some peoples xenia can grow twice the size in one month with low/med flow 
i thourght you had to have places in the tank with less flow so you can place coralst hat dont need as much flow there? but anyway if you want to add another powerhead then you can
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