Equipment

Equipment

Tank($20-$10,000+):
They say, 'The bigger the tank, the easier it is to maintain.' Larger water volumes absorb environmental shifts slowly, giving you a safety buffer. In small tanks, temperature drops and nitrate spikes can happen quickly.
Petco/PetSmart has 20 gallon long tanks regularly on sale for $40. Better to buy new than risk a used craigslist tank(?)
Waterbox has beautiful well crafted rimless tanks if you want something amazing.
Follow the rimless aquarium's instructions for whether a leveling mat is required, rimmed tanks just need to be supported at edges.
Think about what you want to stock and get the tank that suits it. 

Tank stand($100-$5000+):
Water is heavy, a 20 gallon tank can be as much as 245lbs with water, gravel and hardscape.
Research the weight and get/or build an appropriate stand. Also nice for keeping all the fish stuff in one place.
While considering the stand consider placement- access to water, windows=algae and how busy the space is.

Filter($15-$500+):
It's recommended to get a bigger filter than the gallon recommendation on the box says. Like if you have 20 gallon tank get a 30/40+ gallon filter. A little extra filtration capacity can provide useful flexibility. Consider if the animals you want like low, medium or high flow.
Sponge Filter
+ Good for low flow animals
+ Easy, simple, least expensive (might be good to get a battery powered one as a backup incase of emergency)
- Ugly and takes up space in aquarium
- Poor mechanical filtration
Hang on back (HOB)
+ Uses less space inside the tank than sponge
- Needs special rim for unit clearance, still ugly
+ Good mechanical filtration
Do not follow the "monthly throw away filter" advised on some HOB devices- ☠️🐟
Instead replace the "throw away filter" with a permanent bio filter sponge and some bio filter ceramic rings.
Never change all your filter media and replace with brand new "clean" ones!☠️🐟
Canister filter
+ Provides high flow for animals that enjoy surfing current
+ Holds a lot of bio filter media- sponges, ceramic rings etc.
+ Excellent mechanical filtration
- Could leak if hoses are bad (Better to buy new than risk a used craigslist canister?)
- Cleaning means dragging it outside, rinsing trays, every 2-3months(+/-) according to the bioload of the tank
Never change all your filter media and replace with brand new "clean" ones!☠️🐟
Porous rocks (lava rock) act as a "bio filter" giving home to nitrifying bacteria in the nooks and crannies quietly converting ammonia to nitrite and then to nitrate.
Live plants act as a "bio filter" removing nitrates from the water column. Not all plants are equal- floating & terrestrial plants taking CO2 from the air and roots drawing up nitrates, will work faster than fully submerged plants. 

Water skimmer($15):
Attached to output of the filter, keeps the surface of the water clean from "biofilm", looks nicer. Many filters have this built in.

Light($15-$500+):                                                                                                                                                                                      Aquarium plants need around a 6500K light
Hygger LED lights have sunrise/sunset mode, easy option.
You can get a timer and a cheap 6500K light from hardware store.
Turn off lights at night.🐟💤

Heater($15-$100):
Not all fish need a heater but most tropical fish do need someway to keep the water 72-79F. If you live in tropical zone and keep the room that temperature the heater will work less and last longer. Cooler places mean the heater works harder. Good to have a backup heater incase one fails. Also make sure not to cheap out on one that might overheat the fish. Hygger is good.

Chiller(if you need one) ($250):
If the aquarium is in a hot climate you may need a chiller- especially if keeping cool water fish. Most fish tolerate some minor temperature fluctuations.

Net($10):
Good for catching a bully or injured fish. Sometimes recommended when you buy a new fish- after floating bag in water(temperature acclimation) you pour the fish and water into a net (bag water goes into a bucket) so you can add fish without bad bag water.

Syphon with sink attachment($40)
Hygger easy hose to sink attachment(or some other brand) makes

Aquarium tool kit
Angled long tweezers, scraper and scissors($15)

1 "Aquarium only” 5 gallon bucket($4)
For fish emergencies, washing substrate, filter sponges, cleaning, whatever

Power Strip ($7)
For heater, filter, lights etc.

Optional-
a CO2 system and plug in timer($100-$500+)
There are many bundled options. Save money by buying pieces individually. Plants thrive with the addition of C02.- Research!

Additives for plants($12-20+)
a general liquid fertilizer, or specific additive like liquid potassium can make a difference for submerged plants- while fish waste gives them a lot of nutrients some need to be added like iron, potassium etc.