well, first things first. I need advice with the sump. Below is a rough draft of what I had in mind. let me know of any flaws that you might see or any advice to make it better will be much appreciated!!
I see some things I would change in your design if it was me. There are some questions that need to be answered first before we can answer your questions.
BUT I will answer your last question. I would not use check valves in your return lines because algae and other debris can get stuck in the hinge of the gate keeping it from closing when it needs to. People have come home to flooded rooms and dead fish because their check valves failed. Even lines with multiple check valves. If you do use them it is a good idea to have other fail safes.
On to my questions!
1. Does your 400 gallon tank have built-in overflows? This will determine what size pipe to use and how many drain pipes you will need.
2. Have you considered having more than one sump on this tank? This does have an advantage as you can have twice as much media plus more water volume. Also if 1 pump fails you would still have one of the sumps operating and filtering the water until you can replace the pump. The next question kind of goes hand in hand with this question.
3. What size tank were you going to use for your wet/dry sump? Ideally you want the wet/dry sump to hold 15-20% of the display tank volume at all times. For your 400g that would mean 60-80g in the sump at all times. While still having room for the excess water that will drain into the sump during a power outage/pump failure..
4. What exactly do you want to get out of this sump? Such as what functions do you want it to perform? Do you just want it for more water volume and biological filtration?
5. Out of curiosity what are the dimensions of this tank?
I would definitely suggest getting different pumps or another iwaki 70rlt because 1500gph on a 400 gallon tank is only a 3.75x hourly turnover rate. That isn't much at all. People tend to aim for 7-10x hourly turnover rate.
You should read Fmueller's 240 gallon tank build that is here. It is a good read. He did a DIY sump which you could possibly get some ideas from. Though I wouldn't have the returns be through a USJ system.
tank dimensions are: 8'x32"x32"
the overflow box is on one end of the tank and has seven 1 3/4" drains (1"bulkheads). I think I am going to make some durso standpipes using 1 1/4" pipe.
what do I want to get out of this sump?
remove debris from tank, add water volume, biological filtration
I am not using the sump design above in my first post. I will be using a 90 gallon for the sump instead of the 50g I originally planned on using. the design will be similar to this:
water will drain in on the left, overflow onto filter pad, go through bio balls, return to tank.
I will be putting in a plastic screen so that the water runs evenly over filter pad and bio balls.
I am getting ready to order a reeflo barracuda external pump (4300gph) and keep my iwaki 70rlt for a backup just in case something goes wrong with the reeflo.
how much can 1" pvc drain? I was thinking about getting the hammerhead pump for an extra $40 and have 5800gph instead of the 4300gph with the barracuda, but I am not sure if seven 1" drains can handle that much flow.
2x 1" drain pipes will not come close to handling 4300 gph. I'm kinda skeptical as to the whole turnover rate deal, to me its more of a question of how much bio-media capacity the filter has. I think the design on your sump is good but you should plan on the water lvl being higher which means you need a smaller pump and you need to make room for 3 to 4 times more bio media about a gallon of bio balls per 40 gallons of water. Now since your overflow box has 7 holes drilled for pipes I would try and put at least 4 stand pipes in and let 2 of them drain into one filter sock so you would need 2 filter socks or if you have the room 1 sock per pipe. For my 600G I tried to use a 45G sump and my 3500gph pump drained it fast. I had to add a 30G backup water reservoir in order to have enough water to fill the tank up to the lvl where I was getting enough return flow back into the sump to complete the cycle. I also have 4x 2" drain pipes back to my sump when I first had only 45 g of water to pump into the tank. As for internal or external pump either should work as long as you had room for your heaters in your sump.
CHBGator all seven 1" drains will be ran to the sump, not just two.
I am not sure that I will be using the filter socks, just the filter pad. that way I have more room for bioballs. with the sump being 90g I should be able to get at least 10g of bioballs in there. I will post a new design of how the sump will probably be.
sry I misread it the first time. How is the water going to be returned back to the tank? Do you plan on making under gravel jets? thats something I would recommend to keep from getting any dead spots in the tank and having excess food and waste accumulating in one spot and it keeps the same stuff suspended in the water longer so it can be sucked up by your filter. One thing to keep in mind is that 4300 gph is going to create a lot of water turbulence. 3500gph was a lot in my 600 till I downsized the pump.