I would not waste money buying Eco-Complete (CarribSea) nor the very similar Flourite (Seachem), as I'll explain momentarily. As you (Nick) were given a bag free, it's up to you, but here I would point out that both these products are bad for substrate fish. You mention a "catfish" so be careful. With a Betta alone I wouldn't worry, but these products are rough. I was alerted to this several years ago (about Eco-complete) so when I decided to finally try one of these so-called "enriched substrates" I went with Flourite because in my hand it did not feel rough. My corys in this tank developed serious mouth issue, one even lost about a third of its mouth, and I had to remove them. Barbels dissolved on some of the corys, and they all had bleeding mouths. Placed over sand, they fortunately recovered, though the one panda still has only 2/3 of a mouth, but now two three years later he has obviously been eating. I had been warned about this by a catfish importer, but I thought the Flourite was less rough as I say, but not so.
As for the "benefit" of these two substrates, I found none at all. I had the 70g tank set up with Flourite substrate for two years before I tore it down and used play sand, and now two years after that the plants are just as good. I found that I still had to add liquid fertilizers, and was even advised to use substrate tabs, something I would have thought unnecessary. I have come across a number of other aquarists online with similar experiences, so I certainly would give these products a skip on both counts.
As for the vacuuming the substrate, I would assume the reasoning to be the claim by CarribSea that Eco-complete has bacteria in it to break down the organics. It is true that waste settling into the substrate is advisable in planted tanks, because bacteria will naturally colonize the substrate to break down organics. This is the prime source of CO2 for plants. This is what should occur in any planted tank with a plain sand or fine gravel substrate.
As for the filter flow, if it is strong enough to remove all the fish excrement it is way too strong for a planted tank, and probably for the poor fish too. The detritus should settle down into the substrate and provide nutrients for the plants rooted in the substrate, and CO2 is a natural by-product of the breakdown. Snails help by eating the excrement and breaking it down faster for the bacteria to handle. I have severn tanks with relatively small fish (tetra, etc) and I never see excrement on the substrate; a very fine cloud can be raised but that is a very different thing, and it shows that the biology is doing what it should be doing.
Byron.
/www.ebay.com.au/itm/CaribSea-Eco-Complete-Planted-Substrate-9kg-Live-version-Coarse-/261764497702?pt=AU_Pet_Supplies&hash=item3cf2614126
