I think your Ehiem+Ph sounds good, maybe not even the PH, nice & easy flow for blackwater. I have a cascade1000 canister on my 65 and it's ideal flow with just enough adjustment to give it some umph if I want.
You can move the media to the canister, or just run the HOB for a few weeks while the canister catches up. That's what I'd do since a lot of your bacteria are going to be stuck to the walls of the HOB and living in the muck at the bottom of it. Then maybe after three weeks, move the media into the canister, fast or slow, doesn't matter.
Thanks for the info on that--turns out I have the perfect filter then.
Now the problem is.. what to do with the 2x AC70, 1x AC50, and 1x sponge filter? Never really understood why the person I bought it from had to use 2x AC70 + the Eheim 2215 together.
I might convert the old 20g to a planted shrimp tank--use the sponge filter.
But that leaves 3x AC HOBs not in use--which is a massive waste. I might give one of the AC50 or 70 away to my friend who is upgrading his turtle tank, since he's been having problems with maintaining clean water, as his massive RESs eat and poop so much.
You could always put them here on the "swap-n-shop". Don't know if you want to recoupe any money or not, but I'm sure some one could use them. Also your LFS might give you some store credit, I know mine would.