Massive fish death help!

[Ventura]

I have a 75 gallon planted tank that has been set up since August (upgraded from a 47 gal) and moved in November. Got ick in December treated with rid-ick without issue and no deaths. Do monthly water changes usually about 20 gallons worth.
About a week ago i started losing fish. I lost all the of my danios, a couple corys, an otocinclus, a couple black tetras, two madagascar rainbows, and now another rainbow appears to be sick. Most fish show no indication of illness they will just be dead in the tank. A couple i have seen white patches like maybe there is something wrong with their slime coat. Started treating with rid-ick for 3 treatments then changed to melafix for currently 3 treatments. I have done a large water change and gravel vac. Nothing seems to be helping. I still have a couple black tetras and some of my large rainbows left as well as a pleco and 2 corys, a knight goby, and a clown loach.
Water has tested at normal levels with slight nitrates present. I've raised the temp to 79. I have changed my filters too. I am running two eheim canisters on it without carbon (ones a 60 ones a 30).
I'm at a loss as to what to do at this point. Any help would be appreciated!

 

[username]

Your fish are just getting old. It is ok. Don't panick.

 

[Fishfur]

I have to ask, when did you get these fish ? The Oto may have died from lack of suitable food. They are obligate algae eaters, what the Germans call Aufwuchs eaters. Without suitable algae to graze, they rely on biofilm, which takes some months to grow in a new tank. So that might be why he died. They also don't like to be alone, and often die within months of purchase because of how they digest food and how they are caught.

But having so many other fish die so close together seems wrong. Danios are pretty tough as a rule and even if all these fish were purchased together, they would not all die of old age in such a tight time frame.

There is zero point using ick treatment if you don't see ick on the fish. Many ich treatments are rather toxic, especially those based on copper.. not sure about rid ich, I've never used it. I don't think Mela fix is very useful except maybe as a general sanitizing agent in a new tank to help prevent fin rot.

But monthly water changes are not enough. Biweekly would be better, weekly better still. Even with a well cycled filter, fish use up the minerals in water over time, and so do plants. Doing water changes, you are not just controlling nitrates, you are also refreshing the minerals in the water, which fish use for their osmoregulation processes.

When you say water tests at normal levels, what precisely does that mean ? It would be good to have the actual readings of the tests for ammonia, nitrite, nitrate and pH.

 

[Cactuspixie]

Your fish are just getting old. It is ok. Don't panick.

OP has had them 5 months, and you conclude that they are all suddenly dying of old age?

 

[Brookster123]

Sounds like a 35% wc monthly just ain't cutting it man. Think about changing 20 gal a week and you'll prob be just fine, white patches could be fungus which could/would be helped w clean water,' its pretty simple really.. Change water weekly and your tank will most likely thrive, or change water whenever and than buy expensive meds that don't work when all you really need to do is give fish fresh water

 

[AngelFishGirl]

Sounds like a 35% wc monthly just ain't cutting it man. Think about changing 20 gal a week and you'll prob be just fine, white patches could be fungus which could/would be helped w clean water,' zits pretty simple really.. Change water weekly and your tank will most likely thrive, order change water whenever and than buy expensive meds that don't work when all you really need to do us give fish fresh water

+1 to this

 

[xwing]

Could have been an ammonia spike or nitrite. Also a big ph swing. You would be a candidate for any of the three with your monthly wc so switch to 20-25% wc weekly