tank system question (DAS)

Hello. I am new to this forum. I have been using a different forum, but have not been able to obtain some information that I am looking for. Hoping this site might be of some help. I have been in the hobby for a year and a half. I have had 75 gallon reef tank during this time. I purchased an established tank from a coworker that was in need of some upkeep. The person who had owned it hadnt cleaned it in about a year. Amazingly there were still 6fish alive in the tank. Through out time I did weekly water changes until I was able to get the water parameters to normal levels. I have since changed the filtration and lighting and have added corals, live rock and other fish. The tank is doing great. My system is a DAS (dutch aquarium system). It has a closed filtration system built into the left corner of the tank. This consists of 2 seperate filter compartments, and skimmer compartment and a heater compartment. The two filter areas are supposed to contain 2 circular filter/spool pads that contain the "good bacteria" of the tank. Is anyone familiar with these systems??? I have removed these filter pads because I figured out a long time ago that they are just huge nitrate traps and I had tons of algae in my tank which these pads were a big source of. I now have a pump powered protien skimmer in the tank and have a powerful powerhead circulating, and a bio wheel penguin filter. I would like to remove the box that contains these compartments since I am not using them. The middle comparment contains a 1inch tube that runs from top to bottom. The tank also has built in shelves about 2-3 inches fromt the top of the tank that are on the front and back. This was to hold the lights and have everything be internal. The person who I bought the tank from stopped using them because the salt constantly corroded them and the whole thing would have to be replaced. With my new biowheel filter, the water overflow has to fall down about 2 inches before it hits the water. Its loud! I'm trying to figure out how I can filter this system without having to spend additional money. Sorry this is sooooo long. Thanks in advance for any advice. I can post pics of the system if its necessary

I will try and take photos of the filter section tonight. It will be much easier to understand with the photos. The 2tangs came with the tank. They are large,and I hope to upgrade to a larger tank at some point, but they seem to be doing well for now. The tank shot is only of the middle section, so there is more room than what the photo shows. I am very familiar with the tang and tank size discussions on forums! I have tried to remove the box unit that contains these compartments, but it doesnt budge and I dont want to chance breaking something in the tank, thats why I was hoping to find someone with this type of system to see if they had run into the same problem. I will post photos tonight when I get home from work. Thanks for the responses, I appreciate all the input I can get.