It seems the fluid reader is not recognizing the blood magic blood altar as a valid tank. The blood altar does have an input/output tank, so I feel like this should be working.

Seems to work just fine for me:

Note that it takes a while before the BM altar lets inserted life essence through to its internal tank, so maybe you weren't waiting long enough ;-)

Hmm. Let me do some double checking, maybe with a few less mods installed.

so maybe you weren't waiting long enough

I don't think that was it, as it was reporting 'is tank' as false, not just that it was empty.

Hmm. Still having a problem. Blood Magic 2.2.0-66, and Integrated Dynamics 0.6.3 are the only mods I have installed, here is the interface for the fluid reader on a full blood altar.

Could you send me a screenshot as to how the reader is connected to the altar?
What happens if you try to pipe in/out fluids to the altar?

Those are all the ways I tried. All reading the same as my first screen shot.

As for inputting and outputting fluids, it is working with refined storage, but couldn't get the immersive engineering pump to work either. Seeing if I can get dynamic tunnels to do it now.

I haven't really gotten to play with integrated tunnels without crashing yet, but I'm thinking that setup should be slowly sucking blood between the altars. I gave it about 5 minutes with no change in either blood level.

I've tried this with the latest BM dev build, which worked for me.
Could you try using this BM build and see if this works for you?: http://tehnut.info/maven/com/wayoftime/bloodmagic/BloodMagic/1.9.4-2.1.0-504-ss/BloodMagic-1.9.4-2.1.0-504-ss.jar

There might be something wrong with their fluid capabilities in the latest public version, since IE also seems to be having trouble with it.

That was it, thanks! Sorry to waste your time, I should have expected it was something to do with blood magic after the IE pump didn't work.

Probably related to the new/old fluid handling referenced in this ticket, for posterity. WayofTime/BloodMagic#942