Small tanks/bowls without filters really NEED that weekly 100% change no matter how many small changes a week you do because you just can't get all the gunk/ammonia causing debris out any other way. Eventually you will be left with daily spikes of ammonia and your fish will suffer.
Actually 100% water changes aren't that stressful to fish, if you do it properly.. You should never use a net. That is stressful. You should gently scoop your betta up in a plastic solo type cup while you rinse the bowl and decor. You should use their in tank thermometer to match the old tank water to match the exact temp of the new water (running tap) and you should add conditioner and stir it up a bit. An acclimation period of an hour, while the fish floats in the cup inside the bowl and you add a couple tablespoons of new water every 10 minutes will completely remove any possibility of too fast water parameter changes. As long as the cup is opaque, stress from being in the cup is very minimal... certainly a lot less than the ammonia they would have to endure otherwise.
If you are running a filter, you never do a 100% change. It is very difficult if not impossible to try to cycle a tank under 5g. You can try, but it may never fully establish..
Cycling takes up to 2 months and during this time you should be testing daily for ammonia and nitrite and doing an extra 50% change any time either show up. In addition to this a regular 50% weekly change with siphon/turkey baster is needed. First you will see ammonia spike, then you will see nitrites. Eventually, even after a week of no water changes ammonia will stay at 0, then finally nitrites. At this point you should be left with only nitrates, which should be kept <20ppm and the lower the betta by a twice weekly 50% change with siphon/turkey baster. However, you may continually see ammonia show up despite these changes and while the filter will help breed some bb, it may just never be enough to completely eradicate all ammonia.
Last edited by callistra; 03-03-2013 at 06:12 PM.