I posted this in my tank journal but as of yet have gotten no answers. If anyone wants to see more of this set up to get a better idea of my problem here it is:
I have a paludarium with ~ 25 gallons of water in the main tank and ~7 gallons in the sump. The way it is designed I had to drill the tank to plumb the outflow. The outflow is gravity fed. The inflow travels ~ 4' and feeds a water fall. This is my first attempt with a sump / DIY plumbing.
I wanted the water to turn over ~ 3-4 times an hour. With this in mind and not wanting crazy flow I went with a 1/2" bulk head (I really wish I just went bigger.) I went with braided vinyl tubing for the plumbing with barbed connections for ease. I have a danner mag 3 for the inflow and the return line is split with a tee one part goes into the sump the other into the water feature. These both have valves to adjust flow. Here is the original plumbing for the bulk head.
I was getting a lot of the sucking noise so I switched the plumbing from the bulk head to allow air in that way (kinda like a durso) this eliminated the sucking noise.
I originally figured that with the tank and sump I would be dealing with around 25 to 30 gallons of water. I also wanted the tank to turn over around 4 times per hour. That would mean I needed around 100 to 120 gallons of flow coming into the tank. A 1/2" bulkhead should handle ~200 gallons of flow an hour. For this reason I figured a 1/2" bulkhead would be perfect. It still may be but here is the problem I am running into, when the water is pumped into the basin some of the water is draining behind the background. I had anticipated this but not at the levels where it would create a problem. Even with the slightest of trickles coming out of the water feature the outflow still cannot keep up.
In retrospect I should have just drilled a larger bulkhead but I feel it is a little late for that. I also could have gone with a smaller pump. I had figured for around 5' of head but looking into it I probably have closer to 4', this is due to me calculating from the pump and not the top of the water in the sump. The pump I have operates at 270 gallons per hour at a 5' head. I figured that with the return going to the sump and water choosing the path of least resistance this would reduce the output of the pump into the water feature significantly. It probably does but not at the capacity to reduce flow to the 100 gph mark.
Some things I am considering as to why the flow is so low.
1. Maybe the strainer and 90 degree elbow slow down the flow that significantly.
2. I am also considering that I am allowing too much air in the system with the tee for the modified durso. My thinking is if I allow too much air there is not enough room for any significant volume of water to pass. I am considering just getting a valve so I can adjust the airflow entering the system.
3. Have an elbow coming off the bulk head on the wet side so the strainer is completely submerged. I am thinking I would need to do this in order for an air valve to work, otherwise the air would come in from the strainer on the wet side.
Due to the unique design and dealing with such a small volume of water I am having a tough time figuring out what is going on here. I thought when I researched this I had it all figured out ha ha. Any help would be greatly appreciated.