This was why i was wondering whether to sandwich them inbetween two sponges? Will probably put them in my 305 as i am replacing my TT ex1200 woth a Hydor Prime 30
If I were you I would try and find a little fine-mesh net bag to put the things in, and either, suspend that in your tank, or put it in your filter (though I would be worried about it clogging your filter fairly quickly with tat flow going through it.... ) if you want to lower your pH how about peat pack for the filter?
Not wanting a full on black water tank, just something with a nice tinge. I would add a piece of mopani, but the water would be bright yellow within an hour.
You could put the alder cones directly into one of the filter baskets (in tights, of course), but I was recommended by the person that sold them to me to pour boiling water over them and leave for about half an hour (like a week's worth of cones) and add that water to the tank when you do a water change. Works well for the tannins not sure about softening/pH though. Saves getting into your filter all the time. Could also put the oak leaves behind something in some tights under a stone to keep them down so you can't see them from the front but can access them easily.