Simply Koi and More Koi

Hey there,

Has anyone come across what is called nitrate filter (tubes).

Did anyone understand how it works?
Manky do you have any info on the topic or an article?

Okay I found this http://www.theaquariumsolution.com/what-nitrate-filter

so, like anoxic filtration, there is a reduced oxygen within that tube, but what role does alcohol play into this?

Yep, it's part of a series I wrote. The preamble starts on the link below with details of how to build one in the next article complete with a second link to a pictorial description of a complete build.
http://www.mankysanke.co.uk/html/good_w ... pt_15.html

The alcohol in that design is used to supply ethanol which can be used as a nutrient by facultative anaerobic bugs. You could empty a bottle of vodka into koi ponds that use trickle tower nitrate reducing filters but I've never found that to be necessary (or desirable).