I hope I can do this without raising anyones hackles.
Lets start with the fact that this thread turned the OP's Q ijto two. One is can you over dose dechlor during cycling, and the answer to that is yes. On this I would quote Dr. Hovanec, one of the world's leading researcher's on the subject of nitrifying bacreria in aquariums,
Lastly, do not add ammonia-removing products as this just complicates the process – let nature take its course and your tank will be ready for fish.
from
http/www.drtimsaqu...ng/how-to-start
Finally, in regards to bio-media there are basically teo features which determine hoow good any media might be for hosting the bacteria. One is surface area and the other, for lack of a better term, is clogability. By this I mean how easily the media will clog and thus impede flow through. The bacteria need "food", oxygen and carbnate. These are delivered via the water. When media clogs, it blocks the delivery system and the bacteria will first go dormant and then eventually die if things remain clogged.
Fortunately, the bacteria do not live only in the filter, they love almost any hard surface, but especially sybstrate. So even if one unintentionally starts to clog up ones bio-media, more the colonies elsewhere should eventually pick up the slack.
Do not add ammonia removers to bind the ammonia- overdosing with these products will just increase the cycling time.
from
http/www.drtimsaqu...ishless-cycling
Until I see another microbiologist who has done the level of research he has into tank bacteria, I will trust what he says.
Now as for dosing dechlor into established tanks, if it is not possible to overdose dechlor, then I would ask how many of you would be willing to pour a cup of Pirme/Amquel/AquaSafe/Stresszyme etc. into a 10 gal tank? It is one thing to say dosing two or three times the recommended dose wont do harm and another to say it is not possible to dose too much.
Finally, yes you can underdose dechlor during cycling. For bacteria to become firmly established they end up living in a biofilm along with a number of other bacteria, This biofilm provides a defence against chlorine and chloramine ( other things). However, during the initial stages of cycling this biofilm has not yet formed and the bacteria are much more susceptible to these substances. At this point underdosing dechlor would reult in bacterial death which would slow the cycle if not stop it dead in its tracks,