RE: What kind of filter system best for propagating corals?
Allow me to jump in and clarify one fallacy here. A wet/dry will not cause your nitrate to jump up. The purpose of the wet/dry is to produce nitrates as part of how nitrogenous waste is cycled in an aquarium. But on the other hand, live rock produces nitrates too and I haven't seen anyone recommend removing it from a tank. Nitrate is produced from nitrites and ammonia which are far more toxic then nitrates.
The cause of high nitrate levels is not its production, but rather the lack of an environment and bacterial population to continue the nitrogen cycle to the final product in the nitrogen cycle which is nitrogen and nitrous oxide gases. Here is a simplified nitrogen cycle:
Organic nitrogenous waste >>> ammonia >>> nitrite >>> nitrate >>> nitrogen gases.
The finakl step, which is called denitrification occurs in a low oxygen environment such as a deep sand bed or in the deep pores of Live Rock. Its carried out by a bacteria called Nitrospira.
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano