right just took it all apart. thankfully its pretty easy to unhook the filter housing with little mess, I was concerned it was going to be a tricky job.
I replaced the coke bottle with a pepsi bottle as i think its got a better shape and this time round I fixed it in place with rubber hose.
Standard 21.5mm pipe than you can get from B&Q etc fits tightly inside the bottle then I found some old tubing that was slighty bigger than the 16/22 filter hose i have this fitted nicely over the 21.5mm pipe.
The rubber tube also fitted tightly over the filter housing pipe. this is how the bottle is held in place.
This time I made it so the pepsi bottle touched the bottom of the filter housing, I then cut out two notches for the water to escape.
then fitted the ceramic disk. I had a look at the maple diffuser before i took it all apart and it was actually working pretty well, it was giving off tiny bubbles but it was a lot smaller than the fluval disk.
So its all back together and running i'm just having a hard time getting all of the air out of the filter housing. its actually at the top of the pepsi bottle as the water comes in, the filter housing itself is full.
When i turn the filter off i can see the air bubble come back up the hose towards the filter, turn the filter back on and it gets stuck at the top of the bottle again.
Do you think it will push its way out eventually or is there a trick i can get to get rid of it?
cheers for all the help guys.