[slief]

Originally Posted by sensei

Thanks for your thorough explanation, it helps a lot in understanding the skimmer!

I also thought that the height of the water in sump also impacts the head pressure over the pump, so a higher level of water would cause the pump to pull and inject less air to the skimmer??

but I understand that this would not matter and what we are trying is to have a higher level of water in the body of the skimmer to avoid closing the wedge pipe to much, correct?

would it be to much if I have a level of 11 inches in sump?
11" favors me because I need a additional sump to put the 2nd skimmer and I want the new sump to overflow by gravity to my main sump and with this measures everything fits under my stand.

please let me know what you think

At 11” you’d likely have to run the pump speed at a lower wattage otherwise, it might overflow. That said, I am sure it would work OK but you would be limiting your tuning ability since you would have to run the pump speed lower to deal with the deeper sump. And the lower pump speed might work great compared to a higher one but you would never know since you wont be able to test it at higher speeds to have anything to compare to. And I have no idea what speed an 11” deep sump would necessitate just in case you were going to ask that.

The additional sump depth doesn’t really impact the head pressure on the pump. It’s the breakline level inside the skimmer that would impact head pressure on the pump but that isn’t even a concern as it really doesn’t impact the pumps since you tuning the foam density via the pump speed anyway.

In all honesty, I would ditch the 2nd skimmer. It’s not a good idea and it IS going to impact the performance and consistency of the 300 & the 250 resulting in inconsistent performance. I run an SM250 on a 700 gallon system (500 gallon main display) with over 70 fish in it. Several of which are around 10”+ fish including a very large vlamingi and a very large unicorn tank. My SM250 could handle a LOT more load. In fact, I wouldn’t even run a SM300 on my system because it likely wouldn’t be consistent with my load and would be somewhat difficult to tune given the SM300 needs a substantial amount of DOC’s to keep it well fed and consistent. It’s more suited for a 700-1000 gallon display with a truly heavy load than it is a 500 gallon display with a reasonably heavy load. And 2 skimmers would never run consistently on my system with one being my SM250 nor do I think it will on yours.

The issue is that the lack of skimming consistency results in elevated dissolved organics since the skimmers need those DOC’s to build a good foam head to fill the neck. If you have too much skimmer, those DOC’s will be removed quickly and the skimmers will idle along while the DOC’s build back up in the system until there is enough DOC’s to fill the neck with foam again at which point the skimmer (s) will skim well for again for a day or two and then stop producing. And then the cycle repeats itself. It will make it nearly impossible to tune either of your skimmers let alone maintain consistently low DOC’s. You are far better off with one properly sized skimmer that consistently works hard than having too much skimmer that hardly has to work and is inconsistent as a result. It WILL result in inconsistently low DOC’s instead of consistently low DOC’s. And due to these skimmers being truly conservatively rated, you can easily end up with too much skimmer resulting in perpetual tuning issues and inconsistent performance. Trust me, I’ve been down this path before with other customers. I’ve had oversized skimmers on my system before and fought them tooth and nail and dealt with inconsistent performance and overflows as a result of having to run them too wet to keep the consistent. 30+ years in this hobby and several years in the industry has taught me a lot. One properly sized skimmer will serve you and your system far better and result in lower overall DOC’s since you will never remove more than 30% of the DOC’s whether you run 1 properly sized high performance skimmer like the BK or 10 of them. In fact, the single skimmer that is well tuned will maintain better water quality than 2 or even 10 skimmers for the reasons I mentioned above. This is coming from decades of experience. I promise you, less is more in your case!