If it has stayed dry it will be fine for next year. or mix it with normal compost and use as normal. I don't use aquatic compost in the pond. I usually plant them in gravel and then they get their nutrients from the water due to the fish poo etc . saves muddying the water .

Thanks SGB - I'll just mix it through other compost and use it on the borders. I saw a feature on TV about not using compost in the pond a few days after buying this so I didn't use it.
I had hoped that due to it's supposed lack of nutrients I might have been able to use it (with something added) for my ever growing sempervivum collection.