Question about something Matt said in an early podcast show

[dpmamay]

In one of the shows with Matt he said if he had an undergravel filter he would have it so the water is pushed up through the sand instead of it trying to suck the water down because of detrius and other reasons.
My question is what if you have been using it so the water is being pulled down through the sand bed and you now want to switch so the water is being pushed up but now it's 4 months of being the other way? Are there going to be any issues?
Thanks
Daryl

[Rob]

yes, you will likely blow all the caught detritus up into the tank and into the water column. you can do this, but make sure you are ready with some good filters and ready to do lots of water changes...

also, this is not a recommended approach if you are attempting to maintain a DSB, if its a SSB you should be ok, just be ready to clean up the mess before it causes an huge ammonia/nitrate spike

[V]

just quietly rob, did u mince up matt & put him in those famous english pies!
cause i haven't seem him in the TR Hallways since, well since i heard him last!
to the unsupecting, he would be forgiven being wrapped up with daddy duties, but its not nice to mince our friends into pies just cause they had a low SG! even lower than the book he loved to read so much...lol

what happens if someone asks for a chicken pie,? what then? lol