Nobody has really stressed the fact that you can put about any media you want into an AC. If you are like me and your home has no basement, then you have tanks spread all over the place and using a central air system is only possible on a room by room basis.
AT my peak I had about 30 ACs running and I have all sizes. I started buying them when the plastic was thicker and the prices were great. My first AC 100 (aka 20) cost me $9.99.
As for their durability, in about 2002 or 03 I travelled a few 100 miles to a college town to buy, from a graduating senior, a lot of their fish supplies including a 75 gal. tank. As part of that purchase I came home with a used AC 150 (aka 30). It had sponges only in it. I still have that filter running today and with the same sponges until about 2 weeks ago when I repalced 1/2 of them with a block of Poret foam.
A number of years ago I began making changes to my filtration. This was mostly switching to a lot of air driven filtration. I became a big fan of Poret foam and I have a ton of cube filters and Hamburg Mattenfilters. The Poret is a vastly superior form of foam and it comes in a variety of porosities as well as colors. Since then I have been replacing more of the the AC sponges with Poret. I have never used the AC Bio-media. I either threw it out or gave it away. I also have replaced some of the Eheim equivalent in my canisters with Poret as well.
While I have change the media, I am still running 18 AquaClears today and in all of the sizes. I have never had one quit all together. One of the great advantages of the ACs is that they share parts. Even though ACs come in 5 basic sizes, they share motors and even impeller shafts. This allows me to keep spare patys on hand without breaking the bank. I have a few motors,and impellers on the self. I have a box with some spare baskets, lids etc.
There is nly one downside to ACs, imo. That is the plastic can crack if you drop it or bang it hard enough in other ways. Also, the U-tube that connects the uplift tubes and the impeller intake are somewhat flimsy and over time they can chip at the impeller intake end. And yes I keep spare intake parts on hand as well.
When FosterSmith was sold to LiveAquaria, the latter had a fire sale on many things. I loaded up on heater controllers and AC spare parts.
One last observation. I have pre-filter sponges an all of my filter intakes. I used to make these from the AC 500 (aka 110) sponges. I switched to using Poret foam for this when I began using this foam for cubefilters and the Mattens.
I can also report my first hang-on filer was an Emperor 400. It quit after about 8 years. When I replaced it wih the same model I discovered they had made many changes. By then I had added Aquclears to other tanks. That replacement 400 was on the tank for under 2 hours before I removed it, reboxed and returned it. Bad show Marineland. I replaced it with an AC 300 as I had already added an AC 200 to the tank which was a planted 45 gal. community.
My only negative comment re Acs is that Hagen has made the plastic thinner so hold down the price. Well the prices are high and the plastic is a bit too thin. It cracks/breaks easier. But they still run forever if you are a bit more careful.
ps. I have power outages and blinks all the time. Some of the ACs do not restart while others do. Some of then have the water drain into the tank so they need to be reprimed while others do not. Moreover, which filters do what is not constant. find cleaning the impellers and wells sometimes fixes this and sometimes not.
