Dick, I am using a 5/8 inch hose. It was the industrial grade hose ( double wall and thicker rubber.) I have had it in about 2.5 months thus far and only see a bit of slime on it but no degredation of the hose or rubber. I would have gone with the weighted tubing but could not find any around here and I had to run 125 feet of hose to get to where I wanted to put it in my pond. Plus the total cost of the hose was somewhere in the range of $17 from Sams club.
As for the diffuser, I am very happy with the one I have. It gives a good amount of dispersed bubbles and move tons of water without being out of control. The place I got it and the model number are as follows in the link below:
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/9733 I am not an expert on diffusers but I can tell you from what I read a good diffuser has less chance of clogging and produces a uniform bubble pattern where the soaker hose seems to clog up and is not as uniform and the stones from what I have heard also clog more easily. Now others may say otherwise and I can't say it from any experience. All I can tell you is that this diffuser does not seem to clog even when I turn it on and off a few times a day and for the price of only $ 19 it was a good deal.
As for the pump and the entire system, I followed the wiring instructions on the other thread and had the entire system built and in the pond in less than 2.5 hours from the time I got all the pieces from the store. Nice quick and easy and inexpensive. ( left me with more money for the fish and other toys )
I hope that this helps and good luck and let us know when you get it up and running
