Hi all, I purchased a flow hive hybrid about 3 years ago and now want to purchase a second brood box for it.
The bottom box takes 8 standard frames - does anyone know what brood box I need to buy that’s compatible with the hybrid box, or are any/all of them compatible?
I’m in the UK.
Thanks!
Hello and welcome to the Flow forum! 
You need to buy an 8-frame Langstroth deep or medium box, depending on whether you want to run brood and a half, or double brood. Do not buy a British National, it won’t fit. 
Thanks, are the frames that fit the existing box Langstroth deep, medium or jumbo? I’d like to be able to swap frames between boxes so want them the same size.
They are deeps
Good idea too! The only problem is that you end up with a bigger colony, which can be a handful if they ever turn aggressive. I run double deep Langstroths here in the US, but in the UK we did brood and a half in National boxes. I think that Nationals are probably slightly larger volume than 8 frame Langstroths, so if you do double deep Langstroths, you will probably be at about the same hive strength that we used to have in Nationals.
Thanks Dawn, but I won’t be running double deeps, I’m intending to place the new box over the first box, allow the colony to draw the combs in the new frames and for the queen to start laying in it, and then I’ve got a nice easy split.
I watched this video on the Flow Hive YT channel doing a vertical split. It was pretty helpful.
