I also noticed that after a good feed of fry (those i couldnt save) that it totally gets black... so i would say that the colouring of the fecies is directly related to the food inwhich it is eating.... I dont think it is camallanus, as what you are seeing is no diffrent then what ive seen from any fish after eating certain flakes.....

TetraMin and its many off shoots were about the first flake foods on the market. They have updated their formulas many times. That company has also contributed to the hobby and hobbyist organizations in many ways.

In fact, a lot of flake foods now boast of having vitamin C added to the flakes. (I think I saw mention of a garlic flake out too.) It is terrific that vitamins (how about the B complex and E too?) are being added to foods. This means though that we would be well advised to use up a container as quickly as we can (a couple of months?) because once opened and exposed to air and moisture those foods begin to lose the vitamins.

For people who buy flake food in bulk, it might be best to keep most of it in the freezer and just fill a small container for feeding.Of course, figure out how to get the stuff out of the freezer bag without coating the stuff in the bag with moisture from the room air. ;)

This may especially be important for flakes sold by re-shippers, who buy in huge bulk and re-bag smaller quantities for retail in freezer bags.

Wardleys also came out with a terrific line of foods some years ago and seemed one of the more innovative companies around and one of the last American fish food companies. (They put the zebra pleco on their spirulina discs for a while. That was an interesting gaff in that the zebra pleco is either a carnivore or at least a carnivorous scavenger, not a vegetarian. The discus pictured on the regular food used to be from one of my friend's tanks.)

They were bought up by the German Hartz Mountain group and continue to make good foods. A situation, which too often accompanies corporate acquisitions though, is that an awful lot of the old staff were replaced by new people.

I still use Wardley's totally topical and spirulina flakes. Also feed TetraMin, Aquarian,  and several others. There is a hunch among some experienced aquarists that varying the foods (even flakes) given to the fish enhances fertility and health. Variety, even in flakes is good.

I know of people who even mix their flakes together with that in mind. I'm hesitant to open that many containers, preferring to feed from one or two until they are finished.