I always use power filters except on tanks used for breeding or rearing tiny fry so that I don't loose baby fish up the filter tubes. The way I decide what size filter to use is to check what the maximum water throughput is of the filter. In the case of a 30 US Gallon tank I would want the filter to turn over at least 30 gallons per hour. Double or tripple that turnover is much better though. (They can always be turned down a bit if required) I also want my filters to use both noodles and sponge and be easy to service.
it can be done if you are committed to doing at least weekly water changes. it also depends on the species of fish you have. some fish like slow moving water, some like fast. find a care sheet on the fish species you have and find out the water movement they like.
No you do not need it because crawfish are not good swimers and can die if you have that much water.
Yes, even if you have Common Goldfish because its gonna smell super bad...
if they are babies... if they are adults they need a 20 gallon tank. you will need to give them more height then floor space
YES
You can put 3 mice in a 10 gallon tank. It is best to not put 4 mice because the ventilation will not be enough and will smell horrible and possibly cause distress to the mice.
Yes but a big enough tank so about 10-15 gallon tank so the all are separate from each other
Danios or glofish would be a good fish to put in the tank. They are schooling fish which means you would need at least three and I wouldn't put more than 5 in a ten gallon tank.
Definately not in the plural form. A 10 gal tank in use only holds around 8 gals or so. 1 Piranha would be over maximum capacity.. The basic rules are. 1 inch of fish needs at least 1 gallon of water (a Piranha is about a 10 inch fish) Every tank must have a permanently running cycled filter. Every tank needs at least 50% of its water replaced every week.
20
You can but it is cruel and it wont live very long.
you mean in a ten gallon tank? yes, then, if it is a stable tank, and there is a male and a female, then it is possible. that has happened to my 10 gal. before.
The fish are not bad together. But way to many fish for a ten gallon tank. You put one fish for every gallon. They will probly do fine but you will have to clean more.