Hi guys, I'll thank by saying thanks for all the pointers and help with cycling my 100g setup. It looks to be almost ready to go, so I'll shortly be swapping my stock around between tanks. With that in mind, I will end up with a "free" tank. In this case, my first tank, my 20g Fluval tank. It came with an internal filter that included the heater too, it just slips in there. Anyway, I am considering upgrading the filter media in the pump before I re-purpose the tank to try and breed my Odessa barbs in there. I already have some new media to put in there, but being new media, it will need to be seeded. So I am also due to go away for work early next week, for up to 2 weeks. So what I was originally thinking, was once the new 100g has been stocked up, I just put the fluval pump in there, and let it pump away for the next couple weeks, and hopefully when I get back it will be ready to go. Will that work? How will I know if it has worked? Would I then just set up the other tank, and test it with ammonia / API test kit for a few days? There is not much room in that filter for anything. It is a Juwel Bioflow One filter. So there were only some foam blocks in there to start with. Not really sure there is much more I can put in there to help things. Or if it'll even be worth replacing the filter media. It is about a year old now though, and throughout it's life, it has been in a quite heavily overstocked tank.