Filter Questions

Currently we have a 10 gallon tank with two gf (I know, too small, but we set
it up as newbies. We are looking to upgrade to a 30gal soon). Anyway, we have
a ryukin that is probably around 2.5 or 3 inches long, and a black moor that is
about an inch or so. They have a fine particled sand substrate (again, newbie
stuff, I want something a bit coarser than playground sand next time), I keep
an air pump running all the time, and we are currently using a Penguin Mini
with the biowheel. We've had this filter for a few weeks.

In that time, I've noticed that the water has been getting a greenish cast, and
I've had more algae everywhere - is this part of having this type of filter?
Before we had a cheap filter, I think it was an Aquaclear Mini, it seemed to
keep the water clear but we had two of them totally burn out in six months.

I had the greeny-cloudy water, and the past two weeks since the biowheel
started getting more gunk on it, I've noticed that the water flows back into
the tank on the intake side even with a new cartridge in place. The biowheel
still turns freely, but when it is in place the water backs up and down the
intake side. I tested my levels the other day, about three days past a 30%
water change, and had 0 ammonia, 0 nitrites, and 20ppm nitrates. I did another
30% change, and cleaned and inspected all parts of the filter, everything is as
it should be.

Is this normal for the filter? Also, should I use a bigger filter?

Thanks!