Hi Richard,
It's possible the seahorse just prefers to hitch at the top of the tank. However, based on what I know of your tank I honestly don't think that's why it's staying up at the top most/all of the time.
First of all...as you were advised to do before, the clownfish has to go. Period. Secondly, your tank is too hot. You need to bring the temperature down to 76F MAX but preferably 74F. Thirdly, frozen brine shrimp is not nutritional for your seahorse and neither is live brine unless you enrich it with vitamins.
You really should have checked around before buying a 12 gal tank and/or the seahorse BUT since you have it we'll do our best to help you. For a single 3" seahorse a 12 gal tank can be a temporary home for just a short period of time. To make it work you will definitely need to get rid of the clownfish. You will also need to get your own test kits and not rely of the LFS to test your water. Water can foul really fast in a 12 gal tank.
I'm sorry to hear you spent so much money...on the seahorse and on the tank

Unfortunately I think you'll need to spend quite a bit more to give that seahorse a suitable home. I wouldn't do anything less than a 20 gal hi tank for that one seahorse.
Before you spend more money though....take the clownfish out and keep feeding the seahorse ghost shrimp (not brine shrimp). For the price you paid...the seahorse should be a captive bred seahorse and should have been eating frozen food. Ideally, you should try to get it to eat frozen mysis shrimp (Hikari brand is available at most stores).
Again, we don't mean to sound like we're picking on you....but as April said, this seahorse is not happy. It's up to YOU to make sure his conditions improve if it's still possible.
Once the clownfish is out (like today or tomorrow) the seahorse should feel more relaxed. Make sure you have something for the seahorse to hitch to on the bottom of the tank... some kind of fake plant or fake coral or something.
Keep trying to get it to eat frozen mysis shrimp. It's much cheaper than buying live foods for it. Things can hopefully improve for this seahorse, but it's up to you to do it.
If you notice any discoloration or white patches on the seahorse, that could indicate other problems brought on by the high tank temperature. Let us know if you see any strange white coloration now or in the near future.
Best of luck!
Tom