lava rocks?

I have a hydro video and they using a multiflow/ebb and grow style system, except it's top feed. They suggest using a layer of lava rock at the bottom of your bucket to allow more space for root clusters. Is this a good idea? lava rock is awfully dirty. Am I better off just using all hydroton? I already have the lava rock, but it's a bitch washing it.

thanks

why don't you just use rockwool in a flood and drain systemit's easier and not dirty

smalltownDill said:

why don't you just use rockwool in a flood and drain systemit's easier and not dirty

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I have no logical answer other then any pictures or videos I've seen using the mutliflow system showed hydroton. I assumed this was the best choice based on the pictures and documentation.