Need Some Help/Opinions on a subject

[Astus]

So a friend of mine who keeps discus and tetras in the same tank sent me this and I am stumped. I told him to check his params but generally I think it would be the discus to go first as they are more fragile and the tetras are normally very hardy.

"If you know anything let me know. I have had fish for decades so I know a little bit more then most. I cleaned my tank and in less then 24 hours all 7 tetras died. Had them for over a year. The discus are way more susceptible to problematic water. Any thoughts?"

 

[Lupin]

His message is very vague. Ask him the following.

1. Water parameters?
2. What test kit was used?
3. Temperature?
4. Filtration?
5. Any sudden change in his maintenance routine?
6. Dechlorinator is used?
7. Foods and feeding schedule?
8. What tetras are these exactly?

Note a few points:
1. There are various species of tetras. Some can drop dead very easily to a significant change in the environment, some don't. Rummy nose tetras and low quality neons are very prone to dropping dead. Discus on the other hand, slowly become stressed turning very black at some point. Depending on the circumstances and degree of damage, it may be irreversible.

2. Any change in maintenance that also abruptly changes the water conditions will easily kill them. Fish cannot adapt very quickly to extreme changes. I wonder how he exactly maintains his tank and how he cleaned the tank up. Did he do a large water change which he normally doesn't? Did he mess with his pH and hardness levels?

 

[Astus]

His message is very vague. Ask him the following.

1. Water parameters?
2. What test kit was used?
3. Temperature?
4. Filtration?
5. Any sudden change in his maintenance routine?
6. Dechlorinator is used?
7. Foods and feeding schedule?
8. What tetras are these exactly?

Note a few points:
1. There are various species of tetras. Some can drop dead very easily to a significant change in the environment, some don't. Rummy nose tetras and low quality neons are very prone to dropping dead. Discus on the other hand, slowly become stressed turning very black at some point. Depending on the circumstances and degree of damage, it may be irreversible.

2. Any change in maintenance that also abruptly changes the water conditions will easily kill them. Fish cannot adapt very quickly to extreme changes. I wonder how he exactly maintains his tank and how he cleaned the tank up. Did he do a large water change which he normally doesn't? Did he mess with his pH and hardness levels?

Thank you so much Lupin I'll get this information right away.