Sandwiched between the glass and filter frame: the red circle shows a minuxcule Amphipod ( 1.5mm ). It is busy excavating a tunnel to move around the gravel bed... This is why you won't see them out in the open during the day since they only come out at night to feed: when most predators are at sleep. Best time to see any is when the lights turn on: you'd better be quick because they will all find refuge after only 30 seconds !! Amphipods have to be the quickest things around, may they be crawling in or out the live rock or swimming in the open !! Just like Copepods they have their own unmistakable signature: They always swim in a circular fashion !!! Amphipods can reach an adult size of 1cm (3/8th in.) and show a striped coloration when dietary needs are met.
Amphipods can also be seen at dusk whith actinic lighting only
The SBMarine Methodology relies on a Biological Filter and the live rock only serves the purpose of establishing marine life forms (support for Corals, niches for Invertebrates and refuge for Fishes). In other words live rock does not serve the purpose of filtration as in some reef setups. This allows for a - light - use in aquascaping: only use the minimum amount to aquascape. It represents a real benefit in having the largest volume of water possible: especially when using man made live rock alone which is 50% lighter than wild reef rock or in a combination !!! Fishes have more swimming space per tank size and Corals/Anemones more space to grow in. In my humble opinion: live rock filtration capacity is minimal compared to an undergravel SBMarine filter: if you take into account that biofilm and organic deposits soon cover and clog the rocky surface thus preventing any filtration... Some recommend to blow away deposits with a large basker or other means but most of it will resettle eventually. Invertebrates such as Amphipods establish themselves in every crevice and hole possible: they continuously roam the entire aquascaping and perform a thorough cleaning job in and out (24/7) !!! If you add other invaluable invertebrates such as Acorn and Polycheta worms: then you can really establish a very performing setup that simply can't be equaled. The best of all is that this methodology will suit all Marine Life Forms except most SPS Corals. But then you just can't fit everything in a Marine Tank and the incredible choice of specimens is phenomal even when bifing out SPS Corals !!
As a reference don't forget that hammer coral (for example) can reach sizes of dozens of feet in diameter and weigh many, many tons... it can also live almost forever !! By contrast: the largest a Toadstool Coral will ever reach is about three feet in diameter and weigh a few pounds....