I dont think it matters. Bottle says to keep in fridge. But i only started keeping in fridge maybe 6 months ago. Used several bottles stored at room temp
Won't see much results for the first 3 months with sps as it takes time for the coral to learn how to uptake the nutrients. So you have to stick with it. Don't follow the instructions either. Start slow and build your way up. Then maintain your dosing schedule.
Seachem also makes Reef Plus. I'm pretty sure that it is very similar to fuel, but a little less concentrated. You may want to post in the Seachem forum or send them a PM to find out what the difference is.
When I began using it Irefrigerated the 1st bottle then didn't on the 2nd.
I noticed the vitamin smell became more pungent about 2.5-3 weeks in by the end of the bottle it was sour smelling a little but still seemed to work , I noticed no negative effect.
Now I buy one and put a weeks worth in an old bottle to keep out and keep the rest cold .
If you haven't try soaking meaty foods in it in the fridge a few days , Then watch them go nutz!!