Two weeks is not enough time to cycle a tank properly.
Check your water parameters as mentioned above.
Read through my signature link for info on starting out with a new tank.
Get Prime water conditioner to help with your fish in cycle.
Read through this too...
Fish-in Cycling: Step over into the dark side - Aquarium Advice
I just learned about cycling but I already have fish. What now?! - Aquarium Advice
A 125L/ ~33G tank is not large enough for a red tail shark to live a healthy happy life. They need a lot of space to roam, patrol and call their own territory.
You need a liquid test kit to test the water to get accurate info needed to make it through the fishless cycle.
Glad you came here to get some good advice for your new tank. Welcome to the community.