Here read this it will get you searching in the right direction...You can buy a 4dkh solution in the States as well. Probably more accurate and easier than making it yourself
<a href="http://www.fishforums.net/content/Plants-a...wto-854hl-4dkh/" target="_blank">http://www.fishforums.net/content/Plants-a...wto-854hl-4dkh/</a>