Penn-PlaxAX3 Universal Cartridges | Fits All UG Under Gravel Filters (2 Pack)

I got these because I want to try to pry them open and put my own carbon zeolite blend in them. However I decided to use them first as is. I rinsed them thoroughly with luke warm water. Put them on and let them work. Well my water got super cloudy. I thought maybe it was because it was a newer aquarium and wasn't truly established yet. Then I took them off today because I will be medicating my fish, and knowing carbon must be removed I thought perhaps zeolite should be too. I put regular elbows on the uplift tubes and let them work. After a couple hours the water looked clearer. Now about 8 hours later it is significantly clearer. I think that these clouded the water. I can't say that definitively. And perhaps soaking them in water for a time would be better than just rinsing them. Thus I've still given 3 stars. This could just be the type of zeolite in them as well, or it could have just been mine. Or it could be that they have the stuff so packed in there, that there isn't room to properly get all the dust out. I will still be able to use them how I planned. Just be careful about getting all the dust out before use. I will update if I learn anything more from some trial and error.

have a undergravel filter and bought these because others out of stock.didnt fit right so had to rig it

Works great

Took a slight amount of modification to work with my older under gravel filter of another brand. But worked like a champ afterward!

Under gravel filters seem to be going away, but I think it keeps the tank cleaner, these work well

Doesn't fit all tubing.

"Universal" fit for all standard riser tubes. Good price, prompt mailing; fulfilled all expectations.

Great product