That is a wet/dry tower,I would lose the bio-balls and like you said use algae inside instead,,But if you really want to do it right I would lose that setup all together and build a proper sump/refugium, a three section setup that can fit under your stand,and will be a lot easier to work on and clean,,The first section would have a mechanical filter and protein skimmer ,the second section has the refugium with algae and plenium,the third has the return pump external plumbed into it with the auto topper feeding into that section,if you want to add other types of filtration or medias the third is the area I would use them in..... The sump is in three pieces that are joined together with unions and ball valves that if you would like in the future you could take out and modify without having to destroy the whole setup........But to each their own.....best of luck
I agree with Regalblue, I used to have a wet dry setup similar that I converted into sump / fuge. It worked ok however was just a pain to work in or clean. If it was me I would use something around 75gal size tank for sump / fuge on 180. Just make sure whatever you use has enough clearance under stand you can still work in etc.
Cummins..I figured out since i privately messaged you that this might help other people out,You said the door openings on the stand are roughly 19 1/4 by 27 1/2,so you can make a sump that is in three sections that are 19 tall 27 long,by 18 deep,If you do the math,which is length times width times height in inches= divided by 231,you come up with 39.97 gallons per tank,when full,now if you take off two inches of height on the tank,so 19 inches becomes 17 inches to make it easier to work on,that leaves an area of 10 inches to move equipment in and out of the area of your sump through the doors,remember you are going to run the depth of your sump at 10 inches deep in the containers so if you do the math,for each section you will have 22 gallons per section,or 66 gallons overall,,Every inch you go up you gain almost 3 gallons of water,per section..If you cut all of your pumps off you have,the capicity to handle 37 1/2 gallons of water when the water settles and that still leaves an inch on top of that.That is one heck of a capacity..Does that make since,,The size of the bulk heads are dictated by the size of the return pump you choose to use ,4 bulk heads link the three tanks together so the center tank is the refugium,on the water coming into the refugium,have a small 3-4 inch high diverter so you don`t blast the substrate out of it,on the output side,next to the diverter wall I would make a strainer out of the acrylic or plastic trays that seperate 22 or 17 hmr bullets That is to prevent the possibility of any thing blocking or restricting the flow,How is that for recycling,you can make a very clean set up that is easy to work on and is a joy to have,I recommend an LED light for the refugium,remember any heat generated by a light source is going to heat up the bottom of the tank,unless you have ventilation underneath it... the last section which is for the return ,I would plumb the return pump in with pvc over the top,because if you bulk head it through the side you can hear the pump resonating through the sump,I know you could use a piece of rubber or plastic hose,but once you add in a ball valve unions to the mix the flow will suffer,and what about the long term chances of leaking,,IF the pump was to fail,you are in for a headache,If you go over the top of the sump with pvc for the suction to your pump,if anything was to go wrong,unhook your return line pick up the pump give it a twist and anything you need is up and out of the tank,easy to work on or fix.........Good luck,,I know you can buy a glass tank or rubber made container cheap,this sump is made to come out from under the tank if you need to work on or modify it and to be hidden out of the way not beside your tank for all to see,and be tampered with,it is designed to filter and clean your water,effeciently,and in the others water goes around,this one water has to go through,you can put a rock in the return section for holding,or coral that gets irritated [stung or slimed] by another coral,to help it exfoliate,I don`t recommend fish in that area unless you have a big strainer,the reason I say big is if a fish gets stuck to it,the bigger the area the pump pulls from the less suction it has on a small spot so the fish can get way from the strainer .The heater goes in the first section,because of all the circulation,and if you should put live stock in the last section you don`t want the possibility of burning it.If you have any questions PM me,I have made several 2&3 section units like this for friends,they are easy to make,and if you price acrylic,they are actually cheap to make,and you can make filter sock hangers ,probe holders,If you wanted to buy another LED and make the last section a frag tank,If you have a table saw,and a router you can build them in no time The sky is the limit