Be aware purigen does reduce the amount of ammonia produced in the tank, thus reducing what is available to the bacteria. I couldn't care what it does to my water clarity. I would never use a chemical or synthetic form of filter media like that. I see it as a hindrance to biofiltration. My water stays plenty clear with cheap sponges and filter floss. My filterless tank stayed just as clear as any other tank for about a year. Then something happened after I moved it. It got cloudy and all weird. Its still being weird. I'm pretty sure its some kinda microorganism thats doing it though. I've just been ignoring it lol.
I honestly don't care for perfectly crystal clear water, though it happens quite often in my tanks. I view my tanks as little ecosystems in a box. That goes beyond fish and filter bacteria. I prefer there be a decent population of common harmless microorganisms in the tank. These are pretty much always present in tanks, but the amount can very a lot depending on filtration and what not. Abbeysdad if it makes any difference I use foods with high 'binders' if you want to refer to them as that. Wheat in some form is the first or second ingredient on all my foods. If it clouds water at all the microfauna will often consume that.
In an established tank, I guess I'm not concerned with the reduction of ammonia, nitrites, nitrates - anymore than if I was to reduce the bio-load by less stock, better feeding, adding living plants, etc. The bacteria colony(ies) will just adjust accordingly.
Respectfully, I don't think your thinking this through regarding your perceived dislike of synthetic filter media. Sponge material, spun polyester filter floss, ceramic bio-media and plastic bio-balls are all synthetic materials. Everything inside and including your filter are synthetic.
Purigen is a synthetic polymer (aka PLASTIC resin pellets). I'm not certain of the exact polymer type as I purchased it in the bags - it looks like very small polyester resin pellets. I'm also uncertain what gives it the adsorbant properties to attract organic materials that are in solution. I don't believe it can be any kind of coating because it is regenerated in chlorine to 'burn off' the organic material it has trapped.
(actually as I looked at the sponges [previous photo] it was clear to me that to some degree I was already trapping organics from the water [notice the discoloration of the sponges]).
Back in the day, 30+ years ago, I used a Vortex diatom filter to periodically treat my many breeder and grow out tanks. After a few minutes micron filtered water was crystal clear, 'polished' to a degree better than the best fresh tap water or any other conventional filtration...but that whole process is cumbersome with a flow far to great to be continuous. (although a diatom filter running continuously in a sump would be slick!)
When you think of it, this process of removing dissolved organics from the water column is akin to the protein skimmer in the saltwater tank. I don't think removing organics in solution from the water column is a bad thing.
Now co-coincidentally, I was watching several underwater videos of the amazon river. It is a very murky mud hole with all manner of particles in the water. Some of our very worst display tanks are far better than the amazon river on a good day!
So we'll have to admit that we go overboard in filtration and lighting and aquascape to create the surreal more perfect display tank world - not really an accurate biotope. It's fun though! Frankly, I'd be pretty embarrassed to have a mud hole display tank in my living room ;-).
I have to say, today is (yet to be done) water change day. I'm looking across into the other room about 20 feet away seeing the fish swim near the back of the tank - the water is so clear it's as though there is no water in there.
I'd rather not have a cloudy, murky display tank.
I don't wish to diminish the discussion in the other thread on the subject, however since you brought it up here...
With respect to fish foods, after extensive research I concluded quite clearly that foods that use fresh whole fish with little/no flour binder/fillers simply MUST be better for our fish. I learned long ago that feeding bread to birds was not good for the birds as the bread was merely empty calories for them.
I'm betting if we use fish foods made with fresh whole food grade fish instead of stale low quality fishmeals loaded with preservatives that contain copious amounts of rice, wheat, oat, soy flours and/or gluten binder/fillers we'll have healthier, happier fish. Stop feeding your fish bread for awhile and see what happens. The only thing you have to loose at most is less than a dollar cost difference for the container of food!