Root tabs designed for garden use are good when the water level in the soil varies.
Water dissolves the root tabs a little at a time, and the fertilizer gets washed down through the root zone of the plant. When the soil is drier the root tab does not dissolve, so there is some remaining for the next time it rains, or the sprinklers come on.
This is not quite the way it works in an aquarium.
Root tabs for the garden, placed in an aquarium, dissolve in water. Deep under the substrate there is not a lot of water movement. When they start dissolving, but there is not much water movement, the water surrounding the tab gets rich in the various fertilizers, and the tab stops dissolving. Then the water movement (slight as it is) and the plant roots remove the fertilizers (slowly) and the tab continues dissolving. Even if the fertilizer moves upward though the substrate there are usually more roots that will take it in before it reaches the water column, or else the substrate can latch onto the fertilizer. (read about cationic exchange capacity). That works just fine. Plants get the benefit of the fertilizer, and minimal traces get into the water column.
If the tablet is too close to the surface of the substrate, too close to the water column, the fertilizer that dissolves is carried away by the water movement, and can enter the water column.
That's what I was thinking; that some had trouble with the root tabs causing an amonia spike due to not being pushed into the substrate deep enough. Seemed to be the only Logical answer.
Thanks Dianna for your informative post about how root tabs work. You always have very thorough explanations.
So now I completely get it thanks to you and m00se. The tabs have ammonia (err, I meant urea) in them (which I did not know because I didn't take a moment to look into it :redface and if not placed deep enough they can leach into the water column.
Okay...I gotta say one more thing about this guy! The expression after he looks into the book is priceless! I swear I make that face far too often LOL! This will make me giggle for quite some time. Thanks m00se :biggrin: