Thanks for the in-depth answer, @Phil Edwards
NoPox is basically a carbon source to stimulate bacterial growth which causes a reduction in waterborne N and P. It's not something I would recommend for a planted tank as it could easily cause algae issues; especially cyanobacteria.
It [pumice products] will work well in canisters if maintained properly, but your idea of using it in an HOB with low flow and a prefilter would be nearly ideal.
Yes, I took is as such, but it seemed a more stable option than trying to dose impure vodka, methanol or vinegar. It is promoted as offering, essentially, more consistency and, therefore, being more ‘forgiving’ in terms of dosing vagaries. Dosing it directly into an HOB, at very low levels (some experimentation required), might avoid the typical problems with carbon dosing.
I used to work for Brightwell and am pretty familiar with Xport NO3. It's basically an expanded ceramic that's impregnated with sulfur. The idea is you'll get anaerobic zones in the media in which sulfur based denitration occurs. It was really formulated for saltwater systems and isn't nearly as effective in fresh water.
The sulfur aspect is what intrigued me. I was thinking that that Brightwell has harnessed some of the benefits of a sulfur nitrate reactor for conversion of the NO3, while stripping the O2. I’m curious, though: why the need for a pH of >7.5?
Seachem Matrix and De*Nitrate are expanded pumice that does exactly what you described in a similar way to Xport NO3 only without the sulfur. The best way to maintain it over the long term is to gently shake it out when cleaning the filter to remove as much particulate organic matter as possible to keep water flow into the pores.
If I am correct, I believe that Seachem’s Pond Matrix (better than lava rock) is the better option than other Seachem pumice for denitrating media as they are larger pieces with, presumably, longer pathways for better development of an anoxic chamber. Speaking of shaking the pumice; are you aware of a ‘best practice’ for ensuring there is no air trapped in the pores?
Is there a particular reason why you're looking to reduce NO3? I worked in the industry for many years and may be able to recommend a better product to fit your needs.
I have no NO3 issues, right now. They are running in the 5 ppm area. Several weeks ago, after having withdrawn any N dosing several months ago, I re-introduced urea at a daily 1.5 ppm NO3-equivalent rate. NO3 remains where it was before adding the urea.
The reason for the question was to get testimonials on the effectiveness of the two products.