I usually do mine in the early spring before plants are growing and this allows me to clean out the sludge from the bottom and that goes on the flower beds. usually every 3 yrs unless I really have to clean it. the last time was in autumn as the fish were struggling with toxicity levels being very high. cause was a half a dead duck, literally.

unless you have to I 'd wait now until autumn. or when the frog-lets have gone but then many of the plants will be actively growing.