Should I turn down the power filter (slower water current) at night while theyre sleeping?

I ask this because I notice that my goldfish (x 4) seem to be pushed away by water current and they don't seem to be able to 'sleep'. When they 'sleep', do they swim at all? I notice that they'd bump into each other, but not sure if they're sleeping or still playing in dark. (4 fish in 10 Galon tank with mini power filterm see my setup below). My water temp. is 24C - 26C (without heater, its summer here in Vancouver, Canada). I've read that warm water doens't carry as much oxygen... and more water current should gives the water more oxygen right?... now I'm all confused ... should I leave the power filter to High? or lower it?

my filter: http://www.hagen.com/canada/english/aquatic/ product.cfm?CAT=1&SUBCAT=...

my tank: http://www.hagen.com/canada/english/aquatic/ product.cfm?CAT=1&SUBCAT=...

I do turn off the light and let the fish sleep (at 12:00am). I guess they'd have enough sleep.

D_ID=01005950010101 http://www.hagen.com/canada/english/aquatic/ product.cfm?CAT=1&SUBCAT=... D_ID=01030050010101

Unless the 4 fish are very small, a 10 gallon aquarium is too small. Start considering larger, as each goldfish will need 10 gallons or more as they grow. The mini filter will do as long as the fish are small, but it is probably at its limit with the fish load. Don't turn it off as that creates more and worse problems. The goldfish should do fine with the current as they seek their preferred spots. If you feel the fish are getting bounced around, try adding some rocks or other decor to break up the water flow. That size filter shouldn't be a problem in water flow. It might be a good idea to increase the frequency of water changes to keep up with the wastes produced, and to keep the temperature down as summer heats up. Good luck.

All of my fish are only about 1 inch... is 10 Gallon really that small? I've heard that if they live in a smaller tank, they will not grow as big, is that true?
http://www.hagen.com/canada/english/aquatic/ product.cfm?CAT=1&SUBCAT=...

if your mom stacked rocks on your head when you were a child would you grow as tall as you are now, probibly not, but would you be in good health, also probibly not.

for now a 10 is going to be ok ish, but think about it that 10gallon is what 12' wide, what do you do when that goldfish gets to be even 6' long