My fish is dying for no obvious reason! I haven’t seen that ever before, need advice!

[LGart]

Hello, I am new to the forum, but a huge aquarium coop fan for a long time. I have been struggling with fish hobby in my own, don’t have anyone to talk to about that and have been mostly relying on youtubers and fish forums for info and advice. I was ready to give up a lot if times but kept fighting. It is the first time when I am trying to get some help, because I am devastated and don’t know what to do. Obviously my fish was getting sick and died once in a while, but things were pretty good for a while. I even decided to get a few rainbows, because I thought I was ready. For a few months everything was fine. Now I lost two of my female rainbows for no reason. They stopped eating and died. My beautiful male lost interest in food, swims frantically and pokes his nose at the glass. I feel like I am losing him too. Most of my tetras stopped eating, lethargic. One died. Other four look really bad, I am positive they will not make it. The only thing I see is some discoloring and white spots (not ich) on the tales. I have never seen fish dying one by one like this! No ammonia, nitrites at the same level. Ph is 6.6 because of the Co2 injection. Used to be at a higher end. But I ran co2 for more than a year.The only Other thing I have noticed is that  my heater stopped working and when I removed it I saw a crack on the bottom. Could something have leaked in the water. I did a massive water change. I would really appreciate some advice! I just watch them with tears in my eyes and can’t do anything...

[Sandy]

Hi you should probably treat the rest of the fish for fungus and such as if they're new fish in quarantine. Also treat for parasites! Cory has many videos about it and sells the med trio on his website. 

[Daniel]

What temperature is your aquarium?

[LGart]

Hi, Daniel,

the temperature in the tank dropped to 70. Igot a new heater yesterday and plugged it in, but the guy whom I was consulting with, he sells fish meds,  told me to do the water change and not change the temperature for 24 hours. Also he suggested it might be pH burn, because some tetras were Slightly  discolored and had pale spots at the tale. And I run the co2 which can drop the pH and it did to 6.6 which is still in a normal range I suppose? I also stumbled upon Cory’s video where he mentioned stray currents due to filter breakage. Or could it be a CO2 build up? 
And replying to Sandy, I don’t know what parasites to treat for, that is why I contacted the guy who sells meds. There is no visual signs of anything, like fungus or worms. I lost one more tetra today:(

[Daniel]

The reason I asked about temperature is one of the signs of being too cool is lethargy and lack of appetite.

I am not that concerned about the broken heater (other than getting a new one going to warm the water back up).

The CO₂ injection is optional so there is probably little harm in discontinuing that for now.

I don't think I have ever seen pH burn, so I am not sure what that would look like.

Get the temperature back to normal and let us know how that goes.

[LGart]

Ok, I will, thank you! But there is something else in the appearance of some fish that tells me they not going to make it. At the beginning they were just lethargic and not eating. Now, one has some kind of a white spot on the fin and mouth, like fungus, but at least it is still interested in some food. Another, that died yesterday, had a couple of bright white ich like spots, that only appeared right before it died, another has a bulging eye, some have white discolored spots in tail. It seems like all of the diseases attacking me at once. In the other hand the first three died without any physical signs of a disease. Maybe their immune system got weakened due to whatever reason, like stray current or so else, and then they started developing other issues...i have never experienced anything like it. 

[ange]

The bulging eye is likely popeye. It sounds like you have a unilateral case. Luckily it's treatable and its possible for the eye to return to normal.

Do you have any photos of the white spots and discolored areas? That helps more than just the written description at some times. I'm sorry for your losses.

[Sandy]

12 hours ago, LGart said:

Hi, Daniel,

the temperature in the tank dropped to 70. Igot a new heater yesterday and plugged it in, but the guy whom I was consulting with, he sells fish meds,  told me to do the water change and not change the temperature for 24 hours. Also he suggested it might be pH burn, because some tetras were Slightly  discolored and had pale spots at the tale. And I run the co2 which can drop the pH and it did to 6.6 which is still in a normal range I suppose? I also stumbled upon Cory’s video where he mentioned stray currents due to filter breakage. Or could it be a CO2 build up? 
And replying to Sandy, I don’t know what parasites to treat for, that is why I contacted the guy who sells meds. There is no visual signs of anything, like fungus or worms. I lost one more tetra today:(

Internal paracites. I think I'd start ick meds now. If spotting is showing up. Try to share a picture for everyone to see. People on here can help you better! 

[Ben Ellison]

I have often heard lowered temps open the door to a lot of sickness. Where new fish brought in the last few months? How's their poo? I agree the temp is the first thing to fix. I also would consider just running the media trio or salt if it isn't planted. A lot of internal parasites don't mean to kill fish they just want to run them down and feed off them forever. That opens the door to things  like ich.

[LGart]

Hi, everyone, first if all thank you for your help!

Ben Ellison, I haven’t add any new fish since June. Everything looked great all this time. I fixed the temperature and turned off CO2, Charles Harrison, the who I consulted with suggested the CO2 could drop the pH And harm fish. The pH is 6.6 right now which is within normal range I guess. The problem is that most if the fish don’t really show any signs of the disease, except they don’t eat. The two rainbows looked perfect, they just stopped eating and died. 
And I don’t really see any poop at all! I saw some white fluffy stuff coming out if rainbow, but read online that it is not a parasite or worm, it is mucus because the fish wasn’t eating. 
I tried to capture the tetra who shows some signs as best as I could. It’s color is pale, the eyes are swollen and there is a white circle around the eye, pale spotting at the tale. It doesn’t look like ich to me. I treated ich a few times, and the fish was acting normal at the beginning, ut was just all covered with tine white spots.