This is a planted tank forum and I know only a couple of people here have experience in marines, I suggest you visit ultimatereef.net, that's where I've learned about marines over the past few months.
By the way, buy second hand, everything is probably 1/2 to 1/4 of the price new.
There's a few ways to do marines, but the must popular 'berlin' method is:
10% Water changes per week (ish)
Using a Protein Skimmer (some don't)
You can use any type of filter for carbon and rowaphos, although you'll only need small amounts of these
Live Rock, usually 1kg per 10 litres
Some people use sumps (I guess you know what they are) to use all their equipment and filter media
Oh yeah it's imperative you use RO water with special salt - so an RO unit is a great money saver
Test kits, at the start you just need basics like Ammonia, Nitrite, Nitrate, pH, Phosphate. But if you get corals, especially hard ones you need other tests like Alkalinity, Calcium, Magnesium and all sorts
You'd need a Refractometer (much more accurate than a Hydrometer and now a days only like twice the price) to measure the Salinity of the water
Of course you need a heater set to about 24C
Make sure there's no copper in your system as this will kill any invertebrate - even coral
Aah I missed a couple of things - Water Movement, tend to aim for 20-40x tank circulation in powerheads ONLY.
And then there's lighting - You've got the choice of T5, Metal Halide or LED. Try not to use T5 PC as these aren't as good. For your average aquarium with corals you'd want 4-6 T5s (6 would cover Soft Corals, LPS and most SPS) or 1 Metal Halide or a couple of LED strips - not sure about the LED strips really
I've probably missed a bunch of stuff but you really want to get yourself to a reef forum as I've learnt all this from them and my tank isn't even going yet
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