Yes, offhand I know of no products designed to lower KH in a marine aquarium, nor am I aware of any products intended to absorb carbonates from saltwater.
So for the time being, I would just ignore the fact that your pH and calcium levels are running a a little low. Avoid adding any pH buffers or calcium supplements (including Sea Balance) for the time being, and your high carbonate hardness or KH levels will gradually come down as the calcifying organisms in the aquarium remove carbonates from the water. How quickly that happens depends on the number of calcifying organisms in the aquarium (e.g., live corals, coralline algae, calcareous algae such as Halimeda, various mollusks and crustaceans) and how high your KH has risen. For example, the carbonate levels will come down much more quickly in a reef tank with lots of live coral, gorgonia and Tridacna clams than they will in your average seahorse tank. And they will drop faster in a seahorse tank with mushrooms and other soft corals, coralline algae, and Halimeda macroalgae than in a seahorse-only setup that just has a cleanup crew with snails, micro-hermit crabs, and perhaps a few cleaner shrimp.
Once your carbonate hardness or KH has come back down to the normal range, Seagazer, you can then address your low pH and calcium levels. In my experience, the best way to stabilize your pH at the proper level is to gradually adjust it upwards as usual, and then use a 2-part Calcium Buffer System periodically thereafter.
To adjust your pH to the proper range (8.1-8.4) initially, just obtain one of the commercially made products designed to adjust the pH upwards in saltwater aquariums and use it according to the instructions. Such a product should be available from any good LFS that handles marine fishes and invertebrates; they typically include sodium bicarbonate as their primary active ingredient and are often marketed under names such as "pH Up" or something similar. Just be patient when you are adjusting the pH and don’t add too much of the product too soon. Very often your pH won’t budge at all the first several times that you add the product according to directions. That’s perfectly normal, so don’t be discouraged if your pH stays at 7.8 even though you’ve added several doses of the product you obtained to raise the pH. Don’t don’t be tempted to add more of it or to add it more often than specified in the instructions. The product must first overcome the natural buffering ability of the saltwater in your aquarium before I can change the pH level significantly. Typically, you add several doses and your pH doesn’t budge at all, but then the very next dose you add may change the pH dramatically. Since you never know when that critical point will be reached, remain patient and continue to carefully add more of the product as directed until the pH does start to change, and then adjust it to the desired level as gradually as possible.
Once the pH has been adjusted to the proper level, you then add the alkalinity component of the 2-part buffer system. Next you wait a couple of minutes and add the calcium component of the 2-part buffer system. Your pH should remain stable at that pH thereafter and this method also has the added benefit of keeping your calcium level in the proper range as well. For a typical seahorse tank, you can keep it stable at the desired pH by adding more of the 2-part Calcium Buffer System about once a week after your water changes.
The 2-Part Calcium Buffer System that Marcie and some of our other members report works well with their seahorse tanks is labeled "ESV B-Ionic" on the bottles, but it sounds like the Sea Balance you have been using does much the same thing. The alkalinity component of these two-part buffers maintains the carbonate hardness or KH in the aquarium, whereas the calcium component maintains the calcium levels in the proper range.
In short, time should gradually solve your problem with excessively high KH, and once your carbonate hardness levels are back to normal, you should then be able to correct your pH in calcium levels as described above. For best results, I would discontinue the Kent buffer and stick with a 2-part Calcium Buffer System such as we have been discussing instead.
You might also consider posting this question on the Seahorse and Pipefish Forum at reefCentral.com, since reefkeepers must monitor and adjust their carbonate hardness much more carefully than us seahorse keepers. The guys at reefcentral may well know some tricks or techniques for adjusting KH that I am unaware of…
Best wishes with all your fishes, Seagazer!