every one i knows always has internal filters in the tank to polish the water.
the old ehime 1400lph are one of the best, fluval 4`s do a decent job or ebay for 2 of the cheaper powerheads with sponges on them.
depending on what your gunner keep the 3000lph sump pump may not do a good enough job on its own. water turn over could do with being higher.
my set up
tank 7x3x2 about the same amount of water as yours.
sump with 47 ltrs of k1 media, 2x sump pumps 1x 3000lph 1x 2500lph
fluval fx5
ehime pro 2 with 30w tmc uv running inline
2 large internals, just added a 3rd for extra polishing
50% WC every 2 days.
i have 4 rays about to be 5 and a few other bits in there.
i can honestly say i will be adding more filtration in the form of a fluidised sandbed filter in the sump.