liquid fertiliser for in-line fertiliser injector

[brammn]

I hope this is the right forum - if not can someone point me in the right directions please?!

I've bought a dosatron in line fertiliser unit to make feeding the orchids in my greenhouses easier.

Does anyone in the UK have one (or similar) and what do you recommend as the best liquid fertiliser for orchids? I've got some Vitax liquid orchid food, and it will work but it only seems to be available in half litre bottles which isn't a lot so I'm looking for recommendations of something I can buy in bulk...

Thanks

Nathan