Restated: What would be the solution to water flow needs if you cannot have open intakes in the aquarium? Let's assume the overflow can't be breached in order to reach those intakes.

One more time, what exactly do you mean?

I'll use an example. Let's say you have a tank full of sea anemones. We'll make them ritteri anemones because they like lots of water flow. In this tank you don't want a PH, closed loop, or anything with an intake. The OF is fine because it is easy to safeguard an overflow without losing efficiency. How do you get the flow up to, say, 10x flow without using PH or CL?

Use a C/L with multiple inlets to reduce the velocity.the overflow box is still an intake. protect the C/L or powerheads the same way..

I'd assume you'd cover the intakes with sponges.

That goes back to what I was saying about Every tank being different. If you do not want to use Powerheads, consider a closed loop. An intake is real easy to guard. Best thing is T the intake off a few times, then there is little suction at all the intake inlets, not just one. If you flow to much through a sump, regardless of skimmer, your going to introduce microbubbles. part of a sump's design is to be slow enough, add time/passages to let the microbbbles escape.

No, don;t use sponges, Nitrate factories. Use Egg crate. If you have 1 1/2" CL intake, but you split it to T's. you now have 4 intakes, each one had a real low suction. an amemone won't get sucked in if you cover the opening with egg crate.

But were getting off the OP's topic here I think.

Half the problem now seems to be everyone going big display tanks and small sumps. Back when sumps were 1st introduced they were always as big or bigger than the display. Now I am seeing 75 gallons with 20 gallon sumps, which is much too small.

Ya, my 150g with a 300g sump would be strange LOL

Mike: Use a perforated nylon intake strainer on a closed loop. I used to use a 1/2 HP (3600 GPH) pump on a canister filter for 25 gallon tanks of small neons and they could comfortably swim right up to the intake or return when I used a perforated nylon strainer. An anemone could live on one while it draws in 3600 GPH. http://www.industrialnetting.com/filtration_tubes.html

Bandit: Single pass skimmers will work for a FIFO system because most of them use Sicce or Laguna pumps that only move 500 GPH.