use of turboflotor 1000 bactoball facility

hi there i have a rio 400 system with a recently set up refugium containing chaetamorpha. the issue i am having is with a slight nitrate reading of approx 5-10ppm. the system has approx 20 kg of live rock + some live aragamax sand not a deep sand bed just a 1 inch covering. the tank has approx 6 anthias + 6 green chromis +1 medium sized regal all fed twicw a day.
the tank has been set up for about 3 months and has recently had a diatom bloom. my question refers to the skimmer as i have replaced the bactoballs with small similar sized chunks of live rock. as i now have set up refugium should i consider not having any media at all in the trickle tower? i presumed using small bits of live rock as media would of eliminated any nitrate output. any suggestions as i have an assumption that this may cause my slight nitrate value?.ps i water change every week 5 galls with ro. i intend on keeping sps corals eventually an allready have the standard softs. ps lighting is twin 250w halide + twin actinic on main tank. arcadia plant light on refugium.

 

If you can I would increase your sand bed to 4 inches or more. Over time the new sand will be seeded with all the good bacter and help with your nitrates. Perhaps you should cut down on your feeding. Also is your skimmer pulling out the skimmate like it needs to?

Jay