OK, sorry for not replying earlier, didn't see the thread. Sumps is an area I actually love playing with, so here goes (ask any questions on anything you don't understand, or are not dure of)...
As I mentioned in the sump thread below, I would always avoid an overflow box. There are too many things to go wrong, and you can pretty much guarentee, they
will go wrong, and when you aren't there to catch it.
All you need to do is lose syphon or have the pipe blocked a little and the system goes bust.
Similarly I would be a little cautious of a wet/dry filter (I'm assuming you mean like where the filter media is out of the water but water is poured over it to maximise oxygen levels). The moment you have a power cut the media will start to dry up and will lead to an accelrated bacteria die-off. I prefer a sump filtration method that is essentially an open, oversized cannister filter where the water flows through mechanical and then biological and is then pumped back out.
If I was you, on a 200 gallon tank I would have a filter capable of holding 40 to 50 gallons at least. You probably don't need that, but remember you have to have the sump slightly underfilled to allow for back flow once the pump is turned off. I prefer to use cheap tanks for the sumps as it allows for easier partitions and you can see how much crap is accumulating in the sump.
If I was doing it I would have a weir in a back corner leading to a small compartment with a durso stanpipe in it (great invention, practically makes the whole thing silent). Remember to have slits in the weir to prevent fish going on holiday and that the bottom of the slit will be the lowest point the tank will drop to once the sump return pump is turned off.
That durso should lead to the first chamber of the sump. If designing from scratch I would have an emtpy chamber with a couple of baffles (plates in the sump that make the water flow over and under them to seperate the sump into compartments) into the mechanical filtration (sponges, filter wool, I use bio balls for mechanical as well, though the baffles themselves will help a fair amount too).
After the mechanical I would have the water flow over another pair of baffles (under the first and over the second) into the biolgical. For Bio I use Alfagrog, it's relatively cheap - £10 for 15kg - and has a good amount of surface area. On a 200 gallon tank I would try and dedicate at least 30 gallons to alfagrog as that will give a little more leway with moderate overstocking (as will the gas exchange from the water flowing over the weir and into the sump and the extra surface area for gas exchange from the sump).
I would place the heaters in the bio section (no need to have the ugly things in the tank). Another thing I am considering is utilising air pumps to generate more surface tension in the sumps to increase any oxygen levels in the sump water to aid larger fish and the bacteria.
After the bio the water will ideally go through another pair of baffles into a chamber with the return pump which the water back to the main tank. I would recommend either an Eheim 1262 or 1264 for the return pump and err on the side of the 1264 as I use a 1262 on my 150 gallon (6x2x2) and this give a nice flow, though I wouldn't mind a little quicker. I would run the return through UV filtration (you will probably need two Vecton UV25 or UV 30s for that flow rate) and into the tank. I put one outlet at each end of the tank, one at the front and one at the back, to ensure a good flow. If you want to have the outler much below the surface then you will need to drill a whole just under the surface to stop it syphoning all the tank into the sump when the pump is turned off.
Remember that the level of the baffles in the sump that are flowed over (not under) are the working levels of the sump. These must be low enough to allow for the water above the level of the bottom of the weir and the water still in the return pumps to drain back to the sump without flooding it.
As you have water supply and drain already I would also add an auto-top off feature to prevent ever having to do routine water-changes on that tank.
If I have horribley confused you, just say. There is so much that you can learn about building sump systems that it is hard to get it all in one post.
Final point, if you wsnt some expert advice on sump manufacture you can do a lot worse than to chat to the marine peeps at the bottom of the forum. I learnt most of my knowledge from the likes of Navarre. Not everything about the contents of the sump translates from reef to marine too easily, but the basics of getting water out of the top tank into the bottom tank and then back upto the top remain the same.
Hope I helped
Andy
(And if you
really want to go hell for leather, you can always play with an algae turf scrubber...I posted on it in Chit-Chat before, but as is usual with my posts it was too techy and not about a betta flaring or a tetra dieing so it was ignored
)
/www.gerasimov.net/wet-dry_filter.html
