To make sure I understand, you set the tank up last Wednesday and added fish right away? The tank needs time to cycle (or build up nitrifying bacteria) to be able to support life such as fish, inverts and corals.
Fish produce waste (ammonia) that is harmful to them. Cycling the tank allows ammonia consuming bacteria to establish and convert the ammonia to nitrite. Nitrite is also harmful so, the aquarium needs time to build up bacteria that consumes nitrite and converts it to nitrates. Nitrates are basically harmless to fish but high levels can lead to algae issue and be harmful to corals.
So, I think you tried to add too many fish too fast without allowing the bacteria to build up. Nothing good happens fast in this hobby. You’ll need to take it slow and, please, fee free to ask here for advice.
All that said, tell us more about your system.
1. How large is your aquarium?
2. Did you use dry rock, live rock or a combination of the two?
3. Did you use dry sand, live sand or no sand?
4. What lighting do you have?
5. Did you use any bottled bacteria to start the tank?
6. What is your source water tap, well, reverse osmosis, reverse osmosis with deionizarion, distilled?
7. What salt are you using and to what salinity are you mixing the water?
8. And lastly, but IMO most important, what are you water parameters testing at?
- Ammonia
- Nitrite
- Nitrate
- Alkalinity
- pH
- Temperature
