Call me ignorant but I can't figure this one out. I've got a Fortify Alchemy enchant and I cannot put it on armour. Is there a certain type of armour I put it on?
You cannot put fortify enchantment onto armor as that would create a feedback loop, and this was intentionally taken out. Likewise, you cannot make a fortify alchemy potion.
However, you CAN put fortify alchemy onto these pieces of armor:
To do so, just find a piece of gear with the fortify alchemy enchantment on it, and then disenchant it (looks like you have already done this step). From then on, you can now use that enchantment on the previously mentioned gear.
There is a pretty well known trick that you can wear both a Falmer helmet and a circlet at the same time, so in actuality you can get up to 5 pieces of armor with the fortify alchemy bonus.
There is a pretty good table on uesp that shows you what enchantments can go onto what armor.