In a 5 gallon, with no live plants, 40-50% weekly with siphoning is the recommended amount.. with live plants, depending upon type and how many, 30% is the average per week.
It all depends on the amount of live plants (if any).. but a 5 gallon and a 10 gallon is the same with no live plants (at 40-50% per week), and live plants will lower it the same, depending upon how many you have.
Adding snails in the mix, whether it be live planted or non live planted, you will up your water change %, depending on how many snails- the more snails you have, the more you will have to change as they create a very large bio load.
And whenever doing a 40-50% water change, on any size aquarium, it is always safer to remove the fish.
Now, in an established tank that has a certain amount of live plants, shrimps, etc you can get away with even less... but it has to be almost packed full of plants.
I should have been more clear when I said 'planted'. By planted I mean moderately or fully planted not just one or two plants. As an example, here is a picture of my moderately planted 20g which has 6 Serpae Tetra, 4 Emerald Cory, and a couple ghost shrimp. I do a 4g water change weakly, and maintain 0 ppm Ammonia, 0 ppm Nitrite, and <5 ppm Nitrate. I do not vacuum the gravel, at all. I'm looking at introducing some MTS to take care of any dying/decaying plant mater.
As always, the heavier you stock the more you'll have to change weekly, but 2 bettas with a few MTS or pond snails in a planted 10g is certainly not heavily stocked to the point of needing 50% weekly changes.
I look at it this way, in a 10g planted tank I would just have to use a glass sponge to keep the front glass crystal clear, siphon 2 gallons into a bucket, rinse the filter media in tank water as I siphon, then refill with 2 gallons of conditioned water. Done. With say two 2.5 gallon bowls I'd have to fill two cups with tank water, catch both bettas, put them in their cups, remove the heaters/filters or bundle up the cords, carry both bowls to the sink, drain them, rinse filter media, refill, redecorate, put the heater/filter back in (or run cables to power outlet), then move the bettas back into their bowl. ... As you can see, a larger aquarium requires less fiddling each week, and larger volumes of water are more forgiving to mistakes (for example having a family emergency that keeps you away for a few extra days).
I have to respectfully disagree with removing the fish being safer though. The process of catching the fish, removing them from their home, an putting them in a couple oz cup is certainly more stressful than leaving them in the 4g of water that would be remaining in a 10g aquarium (or 2g in a 5g aquarium). Stress weakens the immune system and invites disease and should be minimized as much as possible. In a small 'aquarium' (bowl really) you have no choice since it's impossible to maintain a cycle and you are forced to do 100% changes.
I'm sorry, I don't understand this. I'm not trying to "maintain" a cycle in my smaller tanks; I'd rather do frequent water changes.
Why should a keeper scour everything every week as you have described? Nobody is that compulsive, are they?
Errm, where did I say to scour everything? I just said bring it to the sink and dump it. Presumably you'd have a heater and filter that would need to be dealt with as well.
A cycle is the process of bacteria breaking the ammonia into nitrite, and nitrite into nitrate. Of the three, Nitrate is the least toxic to fish. With no cycle, ammonia begins to build immediately, the rate of which depends on volume. So while a 100% water change will remove all the ammonia, that is only true for a limited amount of time (less than 1 day). Any reading over 0 ppm ammonia is toxic to fish, there is no safe amount.
Since in a cycled aquarium ammonia and nitrite will always remain at 0 ppm, the inhabitants will live longer, healthier lives.
Sorry, Geomancer, I read the scour part in from other posts describing 100% changes.
I'm constrained by space to runnung 2.5g tanks ("bowls," if you will); my split 5g is inconveniently large. That's the one I could cycle, but filter noise and fear of (frequent) power outages keep me at my every-third-day water-change schedule. I never see NH3 over .25ppm and my NO2 and NO3 are, of course zero.
I totally agree with not stressing the fish with routine removal from their tanks. Even though mine are apparently tolerate it well, I'm sure they don't like it much. I siphon and vacuum alll changes, so I don't have the cord bundling, dumping in sink, redecorating hassles.
I'm working up the courage (and finances) to build a 2.5g NPT. If that works, I'll do my 5g.