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Hi, Rj
By "lava sand", are you referring to zeolite or specifically the product ZeoPro? It's purported to have some kind of extraordinary CEC, but from recent conversations with some whose judgment I trust: "... I didn't see results that made feel I can't do without this." There's nothing stopping you from trying it out & letting us know your findings though.
You may also wish to consider substituting a calcined clay product for any perlite in your soils. Calcined clay aggregates (such as Turface MVP) have an excellent CEC capacity (if it means anything, up to 12 me/100 cc) and 40-50% internal porosity. This translates to good water holding capability (over perlite since it has 0 usable internal porosity) and a whole lotta cation attachment sites @ more than 13 acres of surface area per lb of aggregate.
Build your soils and select container sizes so that you can go at least 24 hours between watering in the heat of summer and when the planting is mature. If you do this, you could well be over-potted early in the grow season when the planting is immature & roots have not colonized the container completely. If such is the case, then is the time to use a wick - until you need to water more frequently than you are willing to. At that point, remove the wick to increase irrigation intervals.
Finer sands will increase water retention and can provide enhanced drainage in some soils, but they generally do so at the expense of aeration. What I consider appropriate-sized sand for hort applications is going to be about 1/2 BB size or larger. I've used screened products: coarse silica, crushed granite, pumice, and Turface all extensively with very good results, but only find them necessary in soils that need to be formulated for extended life.
As far as the sand you refer to "facilitating a greater nutrient absorption rate by the roots, I would have to say that is probably technically not accurate. It may be true that it could prove beneficial by holding onto nutrients that can readily go into solution and then be absorbed by the plant, but it won't likely increase absorption over and above what any adequate nutrient supplementation program would. Plants absorb water and dissolved nutrients when the moisture (matrix) tension of soils is lower than the cellular tension and is probably unaffected by what soils are comprised of (structurally speaking - pH assumed appropriate) so long as air/water/nutrients are present in appropriate ratios.
