Seaweed plus sequestered iron

While picking up another gravel tray in the local DIY shop, I saw a bottle of seaweed plus sequestered iron.  Now I remember reading on various threads of the benefits of this for leaf yellowing on ericaceous plants, but not how often it is used.

I have a few camellias (one in the ground and yellowing a bit), kalmia (yellowing a bit), trachelospermum jasminoides (not ericaceous but yellowing.. er.. a bit - you get the idea).

Anyway, the instructions say to apply every fortnight, but I'm sure I've read here that it's used as a 'pick me up' rather than a feeding regime.  

What do people here generally do?