Very true, but if you are running a bacterial driven system eg Bio Pellets, ZeoVit, Vodka etc. a skimmer is a must to remove the bacteria from the system, to benefit from the nutrient reduction that this system provides.
Except for advice right
The problem arises when people apply a technology superficially. You cannot simply drop in a powerhead and check flow off or your list. Setting up a closed loop is even more specific. If you don't know what you are doing you cold have a flood and even worse flow dynamics.
A lot of the people who have traded in their closed loops had undersized intakes, intakes that were too close to the sand, small strainers that were allowed to clog, undersized plumbing (in & out), too many elbows & tees, poorly designed pumps, and poorly planned output/effluent orientation. Sequence Reef Flo pumps have a really poor pressure rating and have discouraged many CL owners. That 3600 GPH Dart pump is cut down to 1500 GPH by the time you push it through all those pipes and fittings (friction loss, not head loss). The limited selection in (magnet coupled) chemical pumps has made powerheads a viable choice for many reefers. Energy savings is another plus, but one that DC CL pumps also offer.
Oceansmotions wave devices are a great tool, but coupled with a VFD you really have something. I like penductors/eductors but for the return line rather than a closed loop as there is a trade off with back pressure loss and venturi gain.
I think the future trend will be laminar flow and pseudokreisels. Laminar flow can be achieved with an intake and return plenum at each end of the tank. A sheet of PVC or acrylic with many holes can be fed or drained by a sealed bulkhead for laminar flow. Adding rounded interior seams to a glass or acrylic tank will help create a pseudokreisel. Having your rock on "footings" will also help water pass under, along the bottom, and back up the front panel. An ornamental cement or foam bottom is also a good tool.
Another method I would like to try is a plenum at the bottom of the tank whereby a series of holes pumps water straight up to the surface zone by zone. This would keep detritus rising and falling in each zone in sequence.
The work of Ken Feldman on protein skimmer efficacy or lack there of is leading us closer to closed systems without sumps. If protein skimmers can only remove 20% of the TOC (total organic carbon), then maybe we should scrap them entirely and spend the (protein skimmer, surface skimmer, sump, plumbing, & return pump) money on better resources. That's a lot of money and energy that can be redirected to more efficient means of TOC reduction. Maybe our protein skimmers should be out in the garage with our bioballs and exercise equipment (as seen on TV)
We can cut down on noise, energy consumption, and floods. We can start sleeping in the same beds as our wives and girlfriends and maybe even go on vacation. Protein skimmers are the only device that require us to have a sump. Sumps add to the system volume, but with a new automated water change system and frequent carbon use who needs it. You can still have extra system volume in a more convenient sealed drum and even grow benthic/cryptic inverts in them. You can take them offline and refill them for hassle-free water changes.
Refugiums can be run very efficiently in sealed canisters like the OceanClear model. I use a clear acrylic top for better light penetration. Ozone can still be added with a reactor or venturi. Heating, cooling, UV, and chemical media are all better served in a closed (vacuum) system. Header tanks (a filter tank located above the display tank) are another viable option.
Beneficial bacteria, calcium, and live food that has been depleted by protein skimmers can be kept in the food chain to feed our reef denizens. Skimmerless tanks have proven to have fewer cases of HHLE (hole in the head lateral erosion) and even reverse the symptoms of infected fish. There are also many reports of better polyp extension.
