Sorry .. didn't wade thru all the replies,
so if this has been said, I apologize.
Odd that the Rena Rep says they are not suited for Turtle use.
Per an online FAQ at PlanetRena.com (
http://www.planetrena.com/Filstar-Rena-FAQ.html )
Q - What is the best media for an aquatic turtle tank? What is the best setup for a turtle tank using the Rena Filstar XP2? What is the difference between the Spraybar and Power Jet Nozzle.
A - With turtles, my goal would be to remove as much solid organics as possible with mechanical filtration, use the biological filtration to keep ammonia levels down and the BioChem Zorb to remove odors and colors which are real problems with turtles. I would also recommend dosing the tank with API Stress Zyme. This is live bacteria that will help break down the solid waste by boosting the action of biological filtration.
You would definitely benefit by having BioChem Zorb in the canister. However, turtle tanks are most known for the large volume of solid organic waste emitted by the critters. You must make sure that you have as much mechanical filtration as you can get. The unit comes with 2ea 20 and 30ppi foams which is about all you can put in the unit. I would use the top basket for BioChem Stars or Ceramic Rings and the upper half of the basket for the BioChem Zorb. I wouldn't use the Micro Filter in this unit since you only have 4 total media chambers.
The Spraybar gives a more gentle agitation of the surface which some aquatic life prefer. However, you won't get as much gas exchange at the surface with this method. The Power-Jet nozzle can be mounted in such a way that it sprays over the surface and creates strong surface agitation that will release harmful gasses from the water and infuses the water with additional oxygen which is very beneficial in breaking down pollutants but not so important for turtles since they don't rely on gills for oxygen exchange.