Any one used CO2 tablet for Aquarium?

I have purchased them and started using them for last 4 days.
I can see good plant growth now.
But before I continue using them, I would like to ask any of you who might have more knowledge in this regard

Are they good? Asking since I can't find much information about them in the net.
Are there any issues?

Thanks
Answers:
CO2 is essential for plant growth. However, uncontrolled release of CO2 into your tank may cause a potentially fatal drop in pH. A change of 1.0 pH is a 10 times change in acidity. Drops in PH are poorly handled by fish and is one of several reasons why you should slowly acclimate new additions to your aquarium.

An alternative to CO2 tablets is Seachem Excel. The product adds soluble carbon for plant growth without affecting pH.

Plants uptake carbon and minerals from the water and their roots. The addition of potassium (K) is an excellent way to spur plant development. See the plant section of fishprofiles.com for more information.

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Adding CO2 to your tank is pretty dangerous. Your fish need oxygen. At night, the plants are aspirating and releasing CO2 as well. CO2 levels spike pretty high in the tank at night.
You can maintain a better balance of gases in a planted tank if you don't aerate it. Aeration robs the water of the gases the plants need during the day.

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As others have indicated their usage can be problematic. I'd say it's time to stop until/unless you get new plants. The only times I use them is when adding new plants (to help with transplant shock and give a boost to initial rooting/growth) or when/unless my plants appear unhealthy (same reason as above) and I only use them at half dosage. And I disagree about not aerating the tank (although I would consider this a personal choice) as IMO aeration's primary benefit is the turbulence helps to maintain healthy gas exchange at the water surface (it's really a topic for another question%26lt;g>).