I have a my betta, pablo, in a 2.5 gallon tank with a small mini heater, a few decorations, some gravel and a floating "betta log" home thing. I just bought him this last sunday, and now that i've got everything all set up i'm wondering how to go about the water changes. Nobody seems to really have a definitive answer of how often you should change the water in a 2.5 gallon tank. i've heard 50% every other day, 25% once a week, and various things like that. I don't really know what to believe. And there's the problem of actually changing the water... how do I take out 50% of his water and then introduce new water and acclimate him to it? do i have to take him out of the tank every time I change the water? and when, if ever, should I change the water completely and like, scrub out the tank and clean off the decorations with hot water? is that necessary? thanks
2.5G uncycled container should have a 100% water change every 4-5 days. The reason you have to do a 100% water change instead of a partial on an uncycled tank is simply that in nature and in larger, filtered, cycled aquariums, the toxic ammonia your fish excretes as waste is converted into a less toxic substance when it is consumed by beneficial bacteria, consumed by plants, and is diluted across larger quantities of water. Since none of these components are at work in your tank, 100% changes are the only way to get rid of all the ammonia and maintain a 0ppm ammonia reading.
If you think about it, if you do one 50% change today and another 50% change tomorrow, this adds up to 100%, but you did not change 100% of the water. Inevitably, some of the fouled water is left over plus whatever your fish contributed in the meantime, so over time, these partial changes become less and less effective.
Here are some simple instructions on how to do a water change:
Put your fish into an alternative container, such as a cup, bag, or tupperware container. Make sure that the container is rinsed clean and has not recently been exposed to soap, and is in a safe place where it will not be knocked over. Remember to put something over it so that the fish cannot jump out. Next, you need to take your tank to the sink and pour out all the water, make sure that you pour the water into a strainer or a colander if there is gravel in the tank--you don't want any of the gravel to go down the drain. Rinse the tank and everything in it with hot tap water so that you get all of the uneaten food, poop, and ammonia residue out of the tank. Then put everything back in and fill the tank up with water that is the same temperature as the old water you took the fish out of--you might want to keep a sample of the old water next to the sink. Dip your hand from the old water to the faucet, adjusting the temperature as necessary until they feel like they're the same temperature, then fill up the tank. Depending on how heavy the tank is, you might want to only fill it partially, put it back on the stand, and then use cups to fill the tank back up if it is too heavy to move. Next, add dechlorinator. Give the tank a good stir and then you can start acclimating your fish to the new water.
To acclimate your fish, float the tupperware/cup/bag that he is in in the tank. Every few minutes, pour out some of the water from his container, and let in some of the new water in increments. If the old water is very similar to the new, (same source, same additives, same temperature) you only need to spread out this process over about 15-20 minutes. If the new water is different in terms of any of those listed variables, and especially when you get a new fish, stretch this out over 30-45 minutes.
Once you get the hang of it, water changes are easy. I find them to be relaxing in a cathartic way. There are some things you can do if you can't stand making frequent 100% water changes--the first is to get live plants. Live plants will help absorb the ammonia, and while they will not eliminate the need for 100% changes alone, they will give you a greater margin of error in case an emergency arises and you cannot change your water according to your schedule. Another thing you can do is get a larger, filtered tank. You can grow a stable bacterial colony in the filter of larger tanks (at least 3G, 5G or larger is great)--this will ultimately convert the ammonia into nitrate, which only becomes toxic to the fish at high levels rather than at any level like ammonia--so you only have to do once weekly partial changes to keep the nitrate in a safe range if you have a filtered, cycled tank. If you're interested in this as a possibility, you will have to research the Nitrogen Cycle and make a few purchases.
DON'T over-clean your tank! I'm a bit of a clean freak, and I used to scrub all my gravel, decorations, and the tank itself, down hardcore with hot water multiple times. Sometimes I even used vinegar to scrub down the tank and decorations, and I cleaned my 2.5 like this every 2-3 days.
This is BAD! Learn from my mistakes I'm still a clean freak that changes the water unnecessarily every 2-3 days (it could really go 3-4, maybe even 5), but now I just stir up the gravel a bit before dumping the water, and I don't rinse my plants or decorations off.
Over-cleaning made my fish start to get sick, so keep your tank clean, but not squeaky clean!
This is just a warning in case you're a clean freak like me
Adastra gives good advice though, so you're in good hands!
2.5 gallon is small, no need to make it more complicated than it needs to be. I don't even use a siphon in my 5 gallon. Every week i replace 10pct of the water by stirring the gravel up first. I then proceed to use the Betta cup that Petsmart uses to house bettas and scoop up water and pour it into a funnel atop a gallon water jug.
My weekly 10pct water changes take less then 5 minutes, and my betta is thriving....