I'm guessing it's not a large enough tank for the goldfish anyway, since if it is you will need to rehome the ADF's. They don't do well at all in tall tanks as they need to go up to the surface for air pretty often, I also think it's possible the water pressure may be bad for for them in deep tanks. Everyone I know who's tried to keep them in a deep tank has failed.
Also, the goldfish will eat the otocinclus, resulting in the death of both fish as the oto will get it's spines dug right into the goldfish's mouths (seen this happen with an oto and angelfish, and a goldfish and corydoras).
22 degrees is not ideal for ADF's, but they can cope with that temperature for a considerable period of time.
Otocinclus on the other hand will die off pretty fast at this temperature, and I've seen whole tanks die when heaters get turned off. Although, they will probably die for other reasons before the temperature kills them.
If you were to turn the temperature up, the goldfish would easily cope with it and ineed thay can thrive with no health problems whatsoever at higher temperatures. However, if you try this you will have a sharp increase in ammonia as their metabolism speeds up and they become even messier fish, probably killing all the fish in the tank.
So IMO there isn't really a safe compromise temperature wise
.
Oh, one last thing, you may also want to tell them that the black moor will probably not work out with the regular goldfish. Sooner or later, it's going to lose an eye or two. I kept these two varieties fine together for about two years until suddenly the common turned on the moor, and this is a very common thing to happen.
