OK thats good, now we have some building blocks
Now Juwels arent designed for sumps (and their stands definately arent) so unless you tell me otherwise i will assume you wont be using a sump.
This will limit your options slightly but its still workable.
This is a 40 gallon tank (UK gallons) so i would suggest 20kg at the very least for filtration purposes.
I would not recomend a deep sand base in this tank for the following reasons. Its limited in space, you will have to place the live rock on the sand and this will cause deadspots in the sand (not a good idea).
I would sugest either no sand at all and have a clean system so waste can be easily cleaned, a thin layer of sand that is no more than an inch deep, or a rubble zone which is made up of grunge live rock and used as a substrate.
As for the internal filter. now this is up to you. you could remove it and gain extra space or keep it in ans utilise the extra water turnover that the powerhead can give you (lots of turnover in a reef tank ) this also gives the added advantage of allowing you to add things like carbon, rowaphos etc if needed.
A protien skimmer would be good for this type of tank. Im not much of an expert with skimmers so i hope that perhaps someone here can recomend a good skimmer for a tank like this. I personally have a Prizm hang on skimmer (i dont use it anymore). The prizm is not the best in the world and to be honest it probably underskims but this is not a bad idea in a natural tank as it means that small trace eliments that would nomrally be removed by a very good skimmer would stil be in the tank for the corals to utilise. However, in this case and example of filtration, its really up to you what type of skimmer you want.
Hope this helps. feel free to ask any more questions if you feel the need
Navarre
P.S.
This is my natural reef system in the Juwel vision 180.
Natural seawater
30kg Live rock
Prizm Protien skimmer (only tun 3 days per week and only then 8 hors per day)
1x 1000ltr per hours powerhead.
1x Internal filter used merely as a powerhead and sponges.
1x Fluval 304 external. Only used for spnges and extra turnover in the tank.
7 redlegs
8 Astrea Snails
1 Copperband
3 Anthias
1 Bluethroat Trigger
1 Bicolour blenny
1 purple firefish
1 coral beauty
1 cleaner shrimp
3 bloodshrimps
1 Algea blenny
1 sandsifter starfish
(many of these have been transferred to the new tank)