This way of starting tanks may not be the best way but I’ve had very little deaths the couple times I’ve done a fish-in-cycle:
1. Dechlorinate the water
2. Dose daily with Stability. You can do it for every day for a week or everyday till the bottle is out. I typically do it everyday until I’m certain the water is cycled.
3. Put some sand/pebbles/decorations/plants from another tank in the new one to help speed up the bacteria cycle. In your case it might be good to buy a plant from your local fish store and put it directly in your tank without rinsing it.
4. Have a few hardy fish in there but not many so while the bad-stuff (nitrate and nitrite and ammonia) starts collecting I’ve never had it get to an actually dangerous level before the cycle starts finishing and the levels of bad go back down.
5. If the bad stuff gets to a high level then do a 25% water change every other day till it’s good again. I recommend these:
For a cheap and nonfussy water test system since your just beginning! *OR* most fish stores will do a free water test if you take a sample of your tank water in store. *AND* new tanks usually have visual indication in the form of algae. When the cycle is starting your tank will become covered with gross ugly brown algae. You can clean if it you want to but you don’t need to. It will slowly fade as the tank cycles and be replaced by a bright green algae bloom as the cycle nears its end. You can wipe it off or have put snails in to eat it (and they will help keep the tank clean in general)
6. Research the fish you got and make sure they are suitable for your natural water parameters (hardness, alkalinity, and ph)
Im assuming the person gave you a complete tank set but here’s a quick checklist:
Substrate: sand, pebbles, or gravel. Sand is the most universal one for fish.
Hang on filter
Well fitted lid
Lights: usually already on the bottom of the lid
Heater: unless your temperature where you live doesn’t ever get too cold, but fast temperature changes can kill fish so a heater just keeps the temp stable. Plus you can change the temp if needed for treatment/different fish requirements.
Air stone and bubbler: gives fish oxygen. keeping the water level a little low so the filter splashes into it can suffice if you can’t get one right away but it’s a bit loud. Real plants also help
Decorations: fish appreciate having plants (real or fake) or caves. It gives them a safe place if they feel scared as well as just giving them things to explore.