First of all a big thank you for the anoxic filter system!

Hello Dr. Kevin.

First of all a big thank you for the anoxic filter system!

I created a modest version of the AFS in September this year (we may move house soon so I wanted to minimize construction work)

I'm delighted to report that the results from 2 black filter boxes (the 1st as a prefilter and the second housing 18 small baskets) has been excellent and I look forward to spring when I suspect the results will be even more rewarding with anticipated plant growth.

Water parameters are good and clarity is good to the pond's 4' depth.

I do have a question though on something entirely different.

For more years than I've kept koi I've always kept an aquarium.

As I'm now in the process of setting up a Nano reef (10.5 British imperial gallons) I'm naturally curious whether the cat litter / laterite combination is effective for salt water set ups.

I wonder whether you have any experience of this matter and whether the combination may work perhaps as a substrate.

Thanking you again for your huge contribution to the koi keeping fraternity.

Kind Regards,

John

Bristol

United Kingdom

In saltwater tanks the substrate has always been a key player in part of the calcium and buffering capabilities for pH and in keeping the water hardness high. The cat litter and Laterite is inert will do none of these. If you were to use it as a substrate like they do in freshwater tanks it would have to be set up as a plenum or have heating cables underneath it to aid in convective movement or by placing the Biocenosis baskets in a sump underneath the tank itself.  A Nano tank does not let you do the later though because of size.

If I was to do a tank like you’re suggesting then a plenum with a height of at least 6.35-19.05 mm from the bottom of the tank and then the medium on top of that.  However, my biggest concern would be the digging of animals into the substrate and not so much the macro and micro fauna that naturally reside in saltwater substrates. But then again in such a small tank not much could be put in it to begin with and fish load would be extremely small at that.  The next thing is you would have to add calcium to the tank like Kalwasser, and then Black algae and slime algae along with cyanobacteria would have to be monitored if a protein skimmer is not used. I think some of those Nano altogether tanks come with a protein skimmer already built into their backs.

In freshwater tanks the setup would be exactly the same except plants would be added to the substrate along with CO2 to aid in plant fertilization cheaper and better than the mediums they sell in pet stores.