Ugh. Pet store employees are the bane of our existence. People who sell these animals and make a profit off their misery do not know a thing about them or the products they sell.
Luckily, you have good instincts and you recognize just from looking at the situation objectively that an unheated bowl and a packet of betta blocks are not adequate for allowing your betta to thrive and live a happy and healthy life.
First thing is first, do you have a dechlorinating product for detoxifying the chlorine, chloramine, and heavy metals in your tap water? If not, I recommend buying some ASAP. Seachem Prime is an excellent brand of dechlorinator, since it is concentrated, the bottle will last longer and you get the most product for your money.
Second, your water changing schedule, I regret to inform you, is going to be difficult in a bowl that small. The simple truth is that fish excrete ammonia through their gills constantly as they breathe, it is their form of waste and it is comparable to urine in mammals. This ammonia is highly toxic and very uncomfortable to be around--you smell it whenever you use cheap window cleaner or multi-surface cleaners. In nature, ammonia is converted into less harmful substances by beneficial bacteria, consumed by plants, and is diluted across much larger bodies of water. Since none of these factors are at work in your bowl, you must compensate by providing your fish with frequent 100% water changes. In a one gallon bowl, you will have to do a 100% change every other day. This seems like a lot, but think about how irritating ammonia is--it can make your fish very sick and cause a lot of suffering if you don't go through with proper maintenance.
Here are some basic instructions on how to change your fish's water:
Put your fish into an alternative container, such as a cup, bag, or tupperware container. Make sure that the container is clean, and is in a safe place where it will not be knocked over, and 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. Do this very slowly and carefully
. If the new water in the tank is different from the old in terms of the water source, the additives, or the temperature, you should stretch out the acclimation time to about 30-45 minutes. If the source, additives, and temperature are the same then the fish only needs 15 minutes or so for acclimation.
If you get a larger tank, (3 gallons or more) and add a small filter, such as a sponge filter, the filter can be colonized by the beneficial bacteria I mentioned earlier and the tank will undergo a process called the Nitrogen Cycle. Once this cycle is completed and the filter is colonized by bacteria (a process that takes about three weeks, during which you have to test your water and do partial changes), you will only need to change 50% of the water once per week. This is a very worthwhile investment of time and money since your betta may be with you for the next 5-7 years if you take proper care of him, and how you choose to house him will have a significant impact on your day-to-day lifestyle. You should research the Nitrogen Cycle and learn about how to cultivate a bacterial colony.
As for the heater, yes, you will need one. The lady at the pet store is a total airhead that knows nothing except that cheap bowls have a higher profit margin than larger tanks with a higher cost value. She doesn't care about your fish, her job is to make the store money and nothing more, and she knows that once people realize that a $3 fish needs a $20 heater they won't commit. I recommend doing as much shopping online as you possibly can. You will save a ton
of money and have access to a much greater variety of quality products. For a heater, I only recommend ones that have an adjustable temperature dial. They cost a few dollars more than presets, heater pads, and other non-adjustables, but again, all these supplies should be thought of as investments
--this fish is going to be with you for a long time, so you want a heater that's going to last and that will give you security, stability, and control. Presets, heater pads, and other cheap non-adjustables are poorly made and do not work on a thermostat, so they will overheat or underheat the water based on the ambient temperature of the room, making the tank vulnerable to dangerous fluctuations, and dangerous temperature extremes. I use and recommend this 25 watt heater: http://www.fosterandsmithaquatics.co...m?pcatid=11368
That online store offers great prices, variety, and very reasonable flat rate shipping. I have seen that same heater for $27 at a pet store, so even if you only buy one, you still save money even with shipping added in. If you buy more items, then your savings really add up quickly. Things you should consider purchasing there include silk plants, thermometer, heater, Atison's Betta Pellets, API Freshwater Master Test Kit, pipettes (they're useful, believe me), and I dunno, just take the time to browse around and see what's out there.
As far as your betta's diet is concerned, betta blocks are awful. They offer little to no nutritional value, cause bloating and complications from overfeeding, and they dangerously pollute the water as they deteriorate in the water. Do not use them. In fact, you should take them back to the pet store and demand your money back--it is ridiculous that she tried to sell them to you as a day to day food item and you shouldn't have to take a hit for that woman's bad advice. If I were you, I'd probably tack on a letter of complaint to the management about their poorly educated staff, but perhaps that's just me, lol.
Onto the real information, you should look for a high quality pellet food--not flakes or freeze-dried or "block" anything. OmegaOne betta buffet pellets, Atison's Betta Pellets, Ken's Betta crumbles, and New Life Spectrum are all great brands. If they are not available, I encourage you to look around and check the ingredients on the back of the bottle. Bettas are carnivores, so meat content is very very important. An ideal food will have some kind of whole meat as the first ingredient, such as whole salmon, halibut, shrimp, krill, etc along with some kind of seafood meal, such as squid meal or fish meal. Generally the more specific the meat and if it is whole versus a "meal" indicates quality of ingredients. If the first ingredient is wheat or soy or corn anything, pass it by. If the first ingredient is some ambiguous fish meal, pass it by. You might want to google the ingredients for the good brands I listed so that you have a specific idea of what to look for. You should be feeding your fish two pellets twice a day, or three pellets once a day to avoid overfeeding--this is just a general guideline, some pellets are smaller than others and some bettas are more active than others and thus, demand more food.
Another thing to keep in mind is that, for bettas, variety is very important. They cannot derive complete nutrition from one pellet brand alone. I alternate between two pellet brands, OmegaOne and New Life Spectrum and supplement my fish's diet with frozen foods like bloodworms, brine shrimp, and daphnia. Frozen foods are high in nutrients but also high in calories, so they should not be your fish's staple. Frozen foods are widely available in pet stores, often there will be a small freezer in the fish section where you can find the foods I mentioned in small packs with "cubes"--I simply cut a cube into fourths (you may need to cut it into sixths or eighths since you have just one betta) with a sharp knife and only defrost what I need for a feeding, this helps eliminate waste. I encourage you to read around on other topics and see what answers other members have found for these similar questions. There's a lot of good information out there, and a lot of bad. Try to read between the lines and look for inconsistencies as best you can.