Which skimmer? 150 gallon heavy stocked
 

Which skimmer would you recommend?

My first suggestion would be a Double Cone 180. If your display is 150 gallons (not including the sump) and you will truly have heavily stocked display which would amount to around 75" worth of fish, then you could go with a Double Cone 200. If your load is lower than you think, you will need to run the 200 pretty wet to keep it consistent.

My goal is 25-30fish

That would likely be a fairly light to medium load unless those fish are particularly large. A heavy load is about 1/2" of fish per gallon. In a 150 gallon display, that would equate to about 75 Anthias or cardinals or a dozen good size tangs.

It would be 4-5 tangs and 20-25 fairy wrasse and anthias

That's a fairly reasonable load. Especially if you keep them well fed. In that case, you can go either way but I wouldn't recommend the Double Cone 200 for anything under a very well stocked 150g display.

So what about until I get it fully stocked that way?

What are the sizes of the necks and bodies of each

The body diameters are 180mm and 200mm respectively. I don't have the neck diameter on hand. If you went with the 200mm, you will likely need to run it pretty wet until you get your stock load up or just live with the inconsistency while you are building your fish stock up. Still, the Double Cone 180 would be perfect regardless of your load. It's a great skimmer and would be very consistent under all loads you could throw at it with that size display. You are better off with a properly sized skimmer that works consistently hard than an oversized skimmer that hardly has to work and is inconsistent as a result. These skimmers are under rated in terms of tank capability so I wouldn't worry about the size of the skimmer when it comes to the Double Cone 180 for your size tank.

Let me ask, since if it doesn't make since to me I am sure other people have the same question. I will be purchasing a bubble king, I just want to make the best choice.

If the cone is only growing by 3/4" and the pump stays the same. The neck maybe grows by 1/4"-1/2". And the same pump.

What makes the drastic change? Please tell. Maybe Royal Exclusive has done the research, and made an actual machine not a pump on a body.

Thank you

The pump speed is what makes the difference as the RD3 is not like any other DC style pump on the market. The RD3 pumps are designed to allow very small adjustment increments which makes for very precise fine tuning. Most DC pumps have only several adjustment points where as the RD3 can be adjusted in single watt increments. The volute and impeller on the RD3 are designed to provide balanced air and water output at any speed. Having the ability to adjust in such fine increments means that one model pump can be used accrossed many different sized skimmer bodies.

Different size skimmers warrant different speed settings on the pump. As the speed increases, so does the amount of water and air being pumped into the skimmer. The 180 sized skimmer performs best with speed set between 18 and 23 watts depending on the amount of dissolved organics in the water. The 200 sized skimmers perform best between 27 and 32 watts. The 250 sized skimmers perform best between 36 and and 38 watts depending on load. When I say best, that means the most dense foam with the least amount of turbulence inside the skimmer coupled with best contact time for the skimmer size. If you run too fast of a speed, you end up with more turbulence, less contact time and bubbles that rise quickly and burst at the surface as opposed to sticking together and making nice dense foam.

I have 30 fish in my 240 gallon tank with a dc200 on it and I skim wetter. He skimmer is a monster, I will add 15-20 more fish and some I have will grow out but I have no doubt the skimmer can handle it.
HTH

Corey