Are you using a savio filter, If so don't use batting before the pre filters, it will starve your pump and cause pre-mature failure. If you want to try something that works far better try Green Matala, THE REAL STUFF! No substitutes on this. It filters better and is easier to clean. Also if you'll put some type of japanese matting or matala under your lava rock ( needs to be one solid sheet per layer but you can add multiple layers if you wish) it will help clear most debris before it gets to the lava rock. this will help the lava rock do a better job. lava rock works good as long as it doesn't clog. I would recommend cleaning the lava rock in a container of pond water twice a year, once in the spring when the water is just starting to get to 50 degrees F and again in the late fall when the water drops below 50 degrees F. this will keep the bio-load stable during the time it's most needed and then the filter falls can just act as a mechanical filter the rest of the cooler months as the bacteria aren't really doing anything once the temp drops below 45-50 degrees anyway.
I run 1 layer of white matala, then 2500 bio-balls, then another layer of green matala in the filter falls and works great even on a fairly heavy stocked koi pond.