Hi, I met the same problem a year ago, I used some strip lights, and they turned yellow very quickly, as a matter of fact in a few months. They weren't bright enough either.
But I did get some new ones for my pond about two months ago, they are still perfect. They are visibly different from my previous ones, since the silicone coating is used within a plastic tube, and they don't turn yellow. Also they are much better in performance - obviously, cause this technology develops rapidly. I would suggest you use these ones I have, because if you mount them high up, it is going to be a pain changing the fluorescent ones.
Here it is, though, strangely the picture of the product is not of the actual product... which is a shame
http://ledcentre.uk.com/index.php?option=com_virtuemart&Itemid=26&category_id=232&flypage=shop.flypage&lang=en&manufacturer_id=0&page=shop.product_details&product_id=319