[Peter Finke]

Patrick, I never said that “fertilizers harm blackwater fish”. I said that one shouldn’t use fertilizers in a blackwater aquarium. Why? What is the difference?
In blackwater tanks you must try to keep a rather delicate stability of milieu conditions as stable as possible. The range of admissable values is much less wide than in a standard tank. Why? Because you must try to keep a water near destilled water as stable as possible. The problem ist the structure of an aquarium tank as opposed to the structure of the natural biotopes. There, you have a constant flow of new waters delivering subsequently water of a conductivity near to nil and a rather stable pH well below 7.0; the very special nutrients for plants (mostly plants of the riparian banks, rarely true underwater plants!) that are stored in the ground don’t disturb that stability because the flow of new water egalizes them again. In an aquarium you have a very small fixed amount of still water, only stired up by a filter pump (sometimes). The filter does not eliminate overdimensioned nutrients. And in most standard tanks they are. You can compare the normal standard aquarium to industrial intensive agriculture. A blackwater aquarium is just the opposite.
In a densely planted tank with mainly underwater plants you need plants fertilizers that constantly renew the level of nutrients. The fish kept there stand that. The success of the aquarium mass hobby wouldn’t have been possible with fish that are not adapted to such changing conditions. The two most important preconditions of the mass hobby – tap water what ever that means and industrial food – include the necessity to have fish at your disposal that can bear that conditions. There are enough blue and red and large and small, as you you know. The licorice don’t belong to that group fitting in the preconditions set by the mass market. Why? Becauses they are adapted to the very special blackwater conditions. Therefore they will never have a future in the aquarium mass trade.
There is another point. Fertilizers are different. For example, some include nitrogens, others don’t. Normally we don’t receive exact informations by the industry what the exact contents are. They talk of “fine plant growth” and that’s it. Such products are risky for aquarists that must try to keep a delicate still water milieu as stable as possible.
And there is a third important point. I always try to convince the friends of licorice gouramis that their first duty is to learn to breed their fish. I think that merely keeping highly endangered fish that have been caught in the wild for beauty’s sake until they die is not the right conduct of a thinking aquarist. There are enough other beautiful fish for them on the market which are produced as mass products. (I don’t like that, but it’s a fact that I cannot change). The first thing one has to learn is to create situations in which those endangered fish not only are ready to breed but in which their eggs and larvae have a real chance of survival and development. And that’s not a tank for which you need “fertilizers”. Nevertheless you can build very nice tanks even full of plant growth. If you look into my small Paro-tanks, each is different. There are plants in all of them. You have the choice of quite some twenty or thirty species. But not of a hundred or more. You must restrict yourself and could nevertheless create highly attractive and different environments. A n d breed the fish. Without using any plant fertilizers (only feeding your fish with that live food and changing waters from time to time).