Yes, you do elicit responses when you post stating you have/propose conditions that hobbyists who truly research their hobby already know are not optimal or recommended.
Your 30g tank would be suitable to move a pair of standard seahorses to as the minimum recommended tank size for one pair is 29/30g, and an EXTRA 15g for each ADDITIONAL pair. This is without other tank mates.
Seahorses need the larger volume because in short time, they "dirty" the water so much that it feed bacterial beds like vibrio species, especially if the temperature is over 74°F. You don't really see the "dirty" but it comes from the eating habits of seahorses in that they masticate the food as they snick it up, passing particulate matter out through their gills and into the water column.
Also, any unseen uneaten food that can be trapped, also provides bedding for the vibrios and low volumes exacerbate the problem.
If you are interested in learning about your new seahorse keeping hobby, and are interested in doing the best you can for your charges, you can read the links at the BOTTOM of the page linked in my signature, "My Thoughts on Seahorse Keeping", written by experienced keepers and by probably the most respected seahorse breeder in North America.
Included in the links there should be a "tank mates" link which if you check it out, will show that garden eels are a threat level four, where zero is good and four is worst case scenario.
http://www.seahorse.org/library/arti...tes/eels.shtml