You don't want to be turning your filter on and off- any bacteria that grows in it, will die when you turn the filter off for a period of time, then be pushed out into the water when you turn it back on. So by you doing that each water change, you're causing the water to become dangerous.
If you go without a filter, unfortunately, you will need to be doing 100% water changes a week in there, so you will mess up your river =( (I believe the person who had done the same thing a while back in the other thread on top has a larger tank with a filter in it so it doesn't need to be taken apart, just siphoned around it.) You can't not do the 100% since you will need to clean out the gravel each week.. and if you do decide to use the filter full time, you will still need to siphon out the gravel. So I would suggest using the filter, and using a small siphon to get as much out as possible without disturbing it too much.
Last edited by Myates; 10-31-2011 at 08:26 AM.