The design is along the same lines as the rest of the Deltec AP range of skimmers.  With a wide diameter main reaction chamber which has a an Eheim 1060 (2800lph) circulation pump bolted to the side of it utilising Deltec's own needle-wheel design, pulling air in through a 4mm wide venturi opening. This is fed via an airline with an adjustable tap on the end to allow adjustment and fine tuning of the air supply to the circulation pump. (occasionally you may find some have the Aquabee 3000 lph pump instead).

The unit is an all enclosed design with a water inlet line (requires a separate 800lph feed pump situated in the sump (usually a 'tapped' Eheim 1250). and an outlet tube so that out flowing water can be fed back to the sump. The skimmer is designed to be used either within the sump, or externally. And the skimmer can be used with Ozone without problems.

At the top, you have a large collection cup capable of holding a good 4 pints of Skimmate, which is secured by a wide necked riser tube, fastened to the main body by a secure bayonet fitting with 'O-ring..( the cup is larger on the later APF851 )

The entire assembly is constructed of very sturdy 'thick gauge' clear and black acrylic. 

Technical specifications.

Rating

Heavy stocking 222gall

Light stocking 333gall

Size... L-390mm x W-310mm x  H-800mm

Recommended feed:  800-900lph

25mm inlet / 32mm return.

Personal opinions.

Well, what can I say about the 850...well quite simply put, I think this is the daddy for systems up to 200 gall no matter how much stock you cram in there. Why not 333gallons as quoted ?, well to be honest, I always like to air on the side of caution and 'over skim' a system rather than push the skimmer to its maximum capacity. Personally, for a 300+ system, regardless of how lightly stocked, Id be looking at the AP702. But going back to the AP850, you wont find a  skimmer in this range that matches it for outright build quality, reliability and above all 'efficiency' in my experience.  On my 200gall system, I was pulling out between 2-3pints of thick dark Skimmate every week end. and the system was pristine.

So what makes this design so good.?

Well, on paper its quite simple to see why to be honest. With a 'feed' of around 800lph, but a 'recirculation' rate of 2800lph, this means, that every litre of water that travels through the body, is crammed through that circulation pump and past the venturi to have air mixed into it more than 3 times before it exits the skimmer body. compare this to inferior all in one single pump models or air driven skimmers and you can see why it has such a large capacity for waste removal.

Setting up the 850 couldn't be easier. All you have to do, is follow the instructions regarding placing your feed pump in the sump, and connecting the outlet pipe so the out flowing water feeds back to the sump. keep the air feed tap turned off and let the skimmer fill up. then 'and only then' turn on the circulation pump. serious note, never ever run a needle wheel pump without water going through it, as severe damage may occur. Make sure that water is flowing freely from the outlet pipe and the internal level is stable.

The best thing then, is to leave the skimmer running in this state (air off) for a good 12 hours if your having to leave it unattended. This will flush out any production coatings. After this period you can turn the air feed on. Personally, I would turn it completely open for the first hour or two, and then throttle the tap back very very slightly to around the 1.oclock  mark.

You'll notice when playing with the tap that the size and quantity of the air bubbles in the reaction changes dependant on how open the tap is. . what your looking for, is a compromise between maximum quantity but the finest size. (usually just shy of fully open.)

Now your away and skimming.

Tips for getting the best  performance:

1. setting the foam break height.

In standard form, many notice that the region where the foam breaks apart to form the Skimmate, is quite low down the riser tube. Which can cause a very dry Skimmate which sticks to the riser tube preventing further foam from rising effectively. This can be alleviated by way of two methods that will both give you a slightly wetter Skimmate that requires the riser tube to be cleaned slightly less often. 1: place a 32mm inline tap in the outflow pipe so you can back pressure the skimmer body slightly. or 2: simply replace the 'supplied' single horizontal section of return pipe with 2x45% adjustable bends which create a slight rise in the outflow pipe, this again creates a small back pressure on the skimmer which will again reset the foam break level to slightly further up the riser tube..

This image shows the settings I have found most successful. With the air tap closed, the running water level should be at the bottom line i.e. just shy of the bayonet fitting. When the air is turned on, the foam level should rise approximately 1/2 way up the riser tube till it breaks at just below the bottom of the collection cup...This will give Skimmate a shorter distance to travel before it drops into the collection cup. Note also the position of the air tap giving rise to a finer bubble structure and better filling of the reaction chamber.(below).

2. keeping it running efficiently.

Every weekend, pull the airline off the venturi pipe (with the skimmer still running) and poke a 4mm drill bit down the venturi. This will clear away any calcium deposits that have built up keeping both the venturi and air supply running at a peak.

Clean the skimmer cup and the riser tube every week using a soft sponge and warm water. I would strongly recommend that a scourer is not used as scratches in the wall of the riser tube will cause friction to the rising foam and will slowly overgrow with algae which will be difficult to remove. Remember that the key to efficient protein removal is getting the foam over and into the collection cup. A dirty or badly abraded riser tube will limit this and lower efficiency. Most people make the mistake with skimmers of leaving it till the collection cup is full before cleaning it. Cleaning it 'more' often, will definitely increase the total amount of waste removed from the system over the long term rather than it suffering periods of inefficiency whilst the riser tube is all scummed up, hindering the rising foam.

Likewise, I would urge that the skimmer is run a in a dark location (unlit cupboard next to the sump). This will prevent the growth of both normal algae and coralline algae on the internal walls of the reaction chamber and lowering of its efficiency..

On an annual basis, the circulation pump should be removed, stripped  and soaked in a bucket for a few hours containing a 6-1 mix of RO water to white vinegar. This will dissolve any built up calcium deposits. After this, rinse off all components with neat RO water, reassemble and then turn back on.

You can find the APF851 at your nearest Deltec stockist.

expect to pay around £400.00 for the skimmer and around £60.00 for an optional fitting kit.