water changes every coupe of weeks would be ok, providing you have a filter. They will be fine with the vibrations, they aren't that sensitive.
As you may know the waste produced by animals & any rotting food produces ammonia. Levels should not rise above 0.25ppm otherise it becomes lethal - even levels that small arent advised. The same goes with Nitrite, which is also very toxic, lastly, nitrate is produced but this is less toxic, and water changes remove the nitrates.
amonia > Nitrite > Nitrate
without a filter, the bacteria (the arrows) needed to convert these toxins cannot develop in sufficient numbers. Also note that plants use ammonia as a source of nitoen, so they will help too.
I reccomend you buy a liquid (not test strip) ammonia and nitrite test kit to test the levels
You can buy a Hang on Back (HOB) filter so that no space is taken in the tank, also cheap
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/www.aquatics-online.co.uk/catalogue...-on-filters.asp"]http
/www.aquatics-online.co.uk/catalogue...-on-filters.asp[/URL]
I am quite surprisd they have survived this long (not offending your skills or techniques). Hpw long have you had them now?