Seahorses are cold water, right? I would expect that the colder water would play into the efficiency of the scrubber. Mainly, the speed of growth. With that considered, one might run into an issue with the lighting level/intensity, if you throw too much light at it then the growth might turn yellow faster/easier than if the water was warmer. So that by default sort of limits the capacity of the scrubber, meaning that you would have to run a larger scrubber under lower intensity to get the filtration you want. But that's just an educated guess.
I guess it also depends on the level of water quality you need. What is the goal with seahorses, I'm not familiar?
I have had discussions about scrubber + seahorses but that was mainly with respect to pod production and the hopes that one could sustain a pod population needed for the constant feeding level required. The idea was, put a huge scrubber above the tank and let it drain directly into it. I think I've read that people do this, they put a large pod refugium above the tank and let it gravity drain so there is a constant food supply, but even that is difficult to self-sustain unless it's well established and even then it has to be replenished regularly.
