Whats the best way to store solution ? Does it have to be kept cold in a fridge or is a cupboard ok

You need to keep it out of direct sunlight and away from heat, otherwise the DHA will weaken. Also you must always keep the lid on tight otherwise if exposed to the air at any length of time, will also weaken the solution. You don't have to keep it in a fridge but keep it in a cool spot. I keep mine in the garage. Solution and last for between 7-9 months depending on brand, but after this throw away, even though the colour guide is there the DHAbwill not work.

Is that opened or unopened?

Opend