I will highlight the top 10 reasons for getting your new aquarium pre-drilled vs. an over the tank set-up using a wet/dry sump system.

10. You do not have to worry about which size and how many U tubes you will need for your overflow box(s). In an Over The Tank Wet / Dry System (OTT-W/D-S) there is an overflow box inside the tank and a pre-filter box on the outside of the tank with a drain tube going down to your sump. To get the water from inside the overflow box to the pre-filter box you use U tubes. There are different sizes and shapes of U tubes and each size has a different flow rate. In the pre-drilled tank there is a filter column inside the tank, no need for U tubes.

11. There is no worry about bubbles in U tube(s) or starting the siphon flow. To get the water to start flowing from overflow to pre-filter box you need to put water inside the pre-filter box and then suck or evacuate the air out of the U tube to start the water flow. If you do not get all the bubbles out, the flow will be restricted and possibly cause your system to not function properly. Also, while in use, you have to make sure no air bubbles are collecting in the U tube as this can cause a system failure. If there are bubbles in the tube you have to evacuate them somehow. In a pre-drilled tank the overflow is built into the column inside the tank, no U tubes requiring intervention to evacuate air and no bubbles to watch.

12. There is no outside pre-filter box so tank can be moved closer to the wall giving you more space in your room. As stated earlier in the OTT-W/D-System there is an outside box which can be anywhere from 3 inches square to 6 inches square. Thus you need to have at least that much room from the back of the tank to the wall, plus 1 inch for cleaning and adjusting the box when system is outside of the tank. In a pre-drilled tank, the drain and return flow tubes are inside the filter column so the tank can be as close to wall as you need or want.

13. The overall appearance of the tank is cleaner from inside the tank, to the top or glass canopy, allowing a better seal over the entire top of the tank. With the OTT-W/D Systems you can not completely cover the overflow box inside the tank, occasionally the glass canopy top has to be modified or water level lowered to allow for the overflow box to sit in the tank and have glass canopy on tank. In a pre-drilled tank the filter columns are inside the tank and glass canopy top can cover the entire tank for less heat loss and water evaporation, also less risk for escape and injury of your aquatic pets.

14. Less dead space in tank. Overflow boxes only draw from the top of the tanks, making dead spaces in the tank. This can create areas where the water does not move and debris builds up. Pre-drilled tanks have the filter column that draws water from the top, middle and bottom of the tank, thus helping eliminate dead spaces.

15. Water returns are inside of the filter column. In the OTT-W/D System the return water flow from the sump is outside the tank and usually hung on the side of the tank either with a directional or water bar sprayer. The hose clamps and plumbing outside the tank can have sharp edges and if bumped can leak or cause damage. In a pre-drilled system the returns are inside the filter column and therefore safely located inside the tank.

16. Filter adjustments are minimal. In the over the tank system you have to adjust the 2 boxes for several variables. One is for the water level inside the tank, height of overflow box, the distance the bottom of pre-filter box is from the back of tank. There may be others to have your system at optimal flow rates. In a pre-drilled tank the filter column has no adjustments, the only adjustment is how much water you want to have standing in the back column, drain tube height.

17. Safer for large fish. The overflow box inside the tank can sometimes be knocked off or dislodged by large fish and can cause the flow to either stop or become too great for the sump pump to handle and cause failure. In a pre-drilled tank there are no filter parts outside of the filter column and cannot become dislodged.

18. Drains are more secure. On OTT-W/D Systems the drains come out from the bottom of the pre-filter. If all the boxes and U tubes are not at optimum settings then the flow will be affected. In pre-drilled tanks the drain is in the bottom of the tank and no adjustments are necessary.

19. Do not lose siphon during power outages or disruptions, no water mess to clean up. In OTT-W/D Systems if power is disrupted and your return flow siphon break hole is clogged or not there, or your overflow box is not adjusted correctly, your tank water level could be affected and cause too much water to empty out of your tank and into your sump, risking possibly overfilling the sump and causing water damage to surroundings. In pre-drilled tanks there is no siphon break or overflow box to adjust.