I bought my tags and tagging gun from Aquatic Ecosystem and used it in our pond for the same reasons as you. If you truly want to look at individual growth over several years I would strongly recommend buying the more expensive individually numbered tags, but if you just want to look at the population as a whole the blank tags will work fine. I tried to mark blank tags but after a year there was algal growth on the tag and I couldn't wipe it off without wiping off the ink. I just caught a bass the other night that was tagged and I haven't tagged any in about 3 years. Some of our fish do show wound marks around the tag but their overall health seems alright. Atleast for me, it has been a fun worthwhile investment.