The water does not have the biological filtration that your media/sand/rock does, so you would probably see a cycle. You can use that media in the HOB
you speak of for the bio-filtration.
Using the water from your DT will be ok, but you want to make sure you still drip acclimate. You can tie the airline tube in a loose "knot" and adjust the drip by making the knot tighter or more loose. I like to do about 2-3 drips per second. I use a ball valve on the end of my tube....
Sorry if I didn't seem clear before.