I wouldn't worry about 0.25ppm ammonia, it shouldn't do any damage. How come your filter got knocked out? 8ppm is really high Had you been away or something? DH accidentally turned the filter off in my big tank once, I was livid. Managed to save all the fish though.
Do you know how long it's been set up? If it's very new then maybe they just didn't cycle it first. If you've got the ammonia level right down then it'll be OK for a while but if the filter's still maturing then you'll need to do water changes every couple of days until everything stabilises. I hope they're bringing you back a large bottle of gin from duty free!
If they set it up and added fish right away then it wouldn't have cycled, it takes about 6 weeks after setting up before it's safe to add fish, although most shops don't know or at least don't bother mentioning it. I'm guessing they do at least have a filter?
This here explains what the jeff is going on in there.
Moving water won't do anything, the bacteria is nearly all in the filter. If you can nab a bit of sponge or filter media from a mature filter then that will really help. How big is the tank and how many fish are in there?