Hello! Matt,
How many and what kind of Seahorses?
If some
LR, dont need much as far as filtration. Look into Supreme SKILTER (both filter and protein
skimmer; I think still avail) if thiking of going small and minimize the cost. Skilter isnt the best but should be OK for Seahorse Tank w/ LR.
Depending on what species and your room temp, heater is something you have to decide.
I just found out local Seahorses (erectus)were spotted near shores in low water temp here.
If thinking of keeping large Brazilian Seahorses, just becareful of small hermit crabs (blue legged Hermits) as i have seen them consumed by Red/Golden/Orange Seahorses.