[craiglanda]

I dont see an issue with keeping seahorses with pipefish. I have succesfully bred kudas and erectus in 30 gallon tanks. The erectus seem to be more readily available where i am from as well as being cheaper than the kudas. So, i would go with the erectus for a first attempt at breeding. However if your willing to wait for the right horses than the kudas can be more brightly colored than the erectus so if that makes a difference to you than as long as they are taking frozen food and dont show any signs of disease, parasites bouancy issues, ect.. than either the kuda or erectus will be nice for a 46 gal. They dont like to much water flow so as long as the powerhead isnt putting out a lot of current you can do like 2 pairs in there. I personally have had succes keeping a pair of males for each female in the tank to rear offspring. It also will give you a glimpse of some behaviors males do during courting. Oh and the mushrooms wont cause an issue to my knowlegde but i personally like to keep sponges or tree gorgonians for them to perch on. You can use fake brightly colored ornaments to try to induce coloration. Aside from what some say about extremly brightly lit tanks will make seahorses more colorful.... i fel thats a myth. MH lights give off much more UV so i found that if not properly shielded these intense lights will cause them to turn black. What happens is the melanocyctes will be expressed as a way to protect their skin from the UV emitted. OK now i am rambling LOL...
There are HOB skimmers you can get so you wouldnt need a sump. i know instant ocean makes one but have no expierence with it so i cant say if i like it or not.