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Welcome back 👍 happy growing 

A quickly tonight had a busy day … hotdog and chips 👍

@BilgePump Thanks for the advice mate, I was a little worried about not using a membrane to separate the sand from the reservoir so it is good to see this confirmed. I had to do some research on that Terram fabric, but that is just what I need, so I will try and get some with the aim of using this just above the Lava rock and below the gravel layer.   Do you have any thoughts on what gravel to use mate, the lechuza pon is very tempting but it is pricy and I worry maybe I am just buying into their marketing, I could also use horticultural grit, it is far cheaper but I worry it may not wick as well and keep that perfect water/air content the way the pon does. I wonder if I could get away with mixing both pon and horticultural grit for this layer.     @mindsoup I have looked at the aquapot tray2grow system and it is/was a strong contender. The one issue was I felt it was a bit small it fits a 1'x3' bed and I really wanted to maximise the size of the grow bed. The set-up above is a 60cm x 100cm bed and is larger than what I could get with the tray2grow. However, that additional volume is mostly being eaten up by the internal reservoir so I am still tossing between the two systems in my mind.     @Military Grade thanks mate, Paint pro over here 😇 Picasso eat your heart out 😂.   On a more serious note, Fungas gnats are a bit of a worry mate, I think provided your bed is healthy and contains a good selection of fauna you will just out-compete them, but I have seen a few beds go south from over watering, so having a water reservoir underneath with stagnant could be an issue. I have been considering running an airline down into the reservoir and connecting it up to an air pump, this might have the benefit of maintaining the biofilter in the lava rock. I think I remember reading something from @Amarillo slim about this. I think he was growing his clones or seeds out on a tray filled with horticultural grit with water at the bottom and an airline running below the grit.   @ipju So my understanding of water movement through capillary action (wicking) is that it is dependent on particle size rather than material. There was a farmer in Australia who did his PhD on growing in SIPs and tested the capillary action of lava rock, compost and sand. All 3 were able to move water, the lava rock was the least efficient and the sand was the most efficient with compost between. If I were going to go with a more traditional SIP with a 4" sewer pipe as my reservoir, I would probably rely on compost to act as my wick with a membrane to separate this from the reservoir. However, I am trying to create different regions within my grow bed and lava rock is a great material to serve as a home for various aquatic bacteria, including serval soil species that are able to convert to living underwater. I hope that by having a healthy population of bacteria in my water reservoir I can keep the water from turning stagnant and anaerobic. Also if there is any run-off from the main bed into the reservoir I hope the bacteria can convert it into usable nutrients for the plants.