if you can put a sponge over the intake/output, you may beable to keep hydroids out, but that won't really help.
With the ten inch height, seahorses are going to be limited, as others are saying. the smaller speices like cold water (less than 70* for capinses) maybe fuscus can do it? but they are VERY hard to find, so I'm told. Kuda just get too big (6-8 inches) erectus and reidi get even bigger at 8+ inches... growing up to a foot tall for reidi, and over ten inches if I remember correctly for erectus.
so, dwarves would be good, and there is one plus being plumbed into a reef tank: the copepods would help feed them. BUT, it needs to be VERY low flow, you need alot of them in a 20ish gallon tank, and your going to be supplementing thier feedings daily with brine shrimp. AND your going to need to keep them out of the display tank, with small screens and things like that.
so, I dunno as to your tank, if it IS suitable for them. You can look at other fish: a peacock mantis would be awsome in there, and he could care less about grasses:he may rearrange for ya, but...
or a jawfish tank, or a firefish tank... leaf-fish are pretty cool and would do GREAT in that tank (they would probably change thier color for ya too even)
