I found bio pellets worked well on my 120. Never tried any other form of carbon dosing as pellets just seem to be the easiest in that you don't have to worry about manually adding a shot of vinegar, vodka etc., or risk overdosing on a doser if it messes up. In setting up my new 45, I'm not sure that I will run them, as I plan on skimming very heavy.
Tony has some valid points, I think people don't use them properly or are too impatient to gradually ramp up the amount they are using, and that accounts for hating on pellets. This is what I've found:
- Pellets/carbon dosing is for REDUCING NITRATES. Regardless of the mechanism of what bacteria does what and feeds off of what, this is the goal of carbon dosing
- You only need a fraction of what is recommended on the packaging - I used about 200 ml on 145 gallons of system water, anymore was counter productive
- Too much carbon feeds cyanobacteria, and creates an issue that needs to be rectified (the obvious is to back off the pellets). The other potential factor is too much flow as Tony noted. I found mine were best at a slow roll. Basically enough flow so they were moving around and not stationary, but definitely not boiling.
I think people put too many pellets online at once, cause their nitrates to plummet and stress out their coral or starve them, promote cyano bacteria growth, decide they've had poor results and then complain that the pellets are to blame. My advice for anyone considering pellets or other sources of carbon dosing would be first measure your nitrates and determine if its a problem. Also, know what levels of nitrate is an issue - 5 ppm of nitrate is not necessarily a bad thing even in an SPS tank. If your nitrates are ok, but you want to increase your feedings, consider carbon dosing as more feeding is likely to lead to more nitrates. When you go online, start with no more than 1/4 of the recommended amount as per common instructions. Monitor nitrate levels over a couple of weeks (I think people skip this part). Slowly adjust upward if needed - i.e. don't bump up if your nitrates are at 0! Keep monitoring nitrates as you bump things up slowly, over weeks, not days!
In short, I think pellets and carbon are a great source of reducing nitrates and is one more nutrient control tool in the box, allowing us to feed fish more heavily without adverse effects to corals or promoting algae growth, within reason. However, like everything else, they have to be implemented with an understanding of what they are for. Similar to over/under feeding and skimming, they are something that can be out of whack and need to be adjusted based on testing and careful observation. You simply don't put a reactor online with 500 mls of pellets in it because the package says so and your local LFS guy says its will make your coral colours more pretty.
