Fish gradually dying off

[The Lost Tapes]

My 75 gallon tank that I have had established for about 4 months has recently been having issues. At some point in mid October I introduced a sick fish to the tank. After a round of medication however, yes the sickness was gone but all of my fish started becoming lethargic. This is where it gets weird for me. So over 2 days I did 50% water changes each day as to get rid of the medicine. However I had to continue doing these changes about every 2-3 days due to the fish going up and gasping/acting lethargic. During this I also had bubbles consistently at the surface which I eventually got rid of by having to clean everything in the tank including the filter. Now I know the filter should not normally be cleaned but I figured out via elimination that whatever was causing the foam on the surface came from it as everything else was cleaned by then. During all of this I had continually lost fish every single day. These were hardy fish as I kept them from when I initially cycled the tank, so by this point all of my White Cloud Minnows had died, 5 mollies/platies had died and several other less hardy fish with it too. So this brings me to now. Most of the issues I had I fixed, but this unfortunately uncycled the tank. So I have been recycling the tank but now something is lowering my PH to 6 or lower. I use the API freshwater test kit. This is all rather long but I am completely stumped as to what is happening as I have essentially tried everything I could think of. I never had any of the PH issues I currently have when I initially cycled the tank. I dose 1-2 teaspoon of Alkaline buffer every day and yesterday my PH was about 7 and today it dropped to 6.

I change about 20% of the water weekly
Ammonia: 8ppm
Nitrite: 0ppm
Nitrate: 20ppm
tank temp: 83
I have Fluval carbon media in my filter
No fish have been added since the aforementioned sickness
Fish are all acting "normal" but it seems one dies randomly
Nothing new has been added to the tank since about September
I use prime to dechlorinate, I dose Stability bacteria every day to try and establish the cycle again.

Apologies if this is long.

 

[Bruce Leyland-Jones]

So your treatment of your poorly fish appears to have completely killed off all of your beneficial bacteria and now you're attempting to cycle the tank once more...with fish present.
Cycling a tank with fish present rarely works out and nearly always ends up with fish dying a horrible death.

NOTE that ammonia levels should be zero...always.
Ammonia burns the skin and gills of the fish.

To climb out of the hole you've found yourself in, you need to change at least 50-75% of the water on a daily basis, until your ammonia is at zero.
Keep on with the bottled bacteria and leave your filter alone...AFTER you've removed the carbon.

Get a load of fast-growing plants and throw these into the tank. These will help consume the nitrogen-based toxins. Floating plants and common pond weed/Elodea are particularly good for this. Here is a list of fast-growing plants. NOTE that I'm not talking about making the tank look pretty with aquascaping at this point, I'm just trying to help you save your fish.

Read and study this potentially useful article on cycling.

 

[Colin_T]

Hi and welcome to the forum

Is the ammonia level actually 8ppm?
If yes, then you need to get it down asap. The best way to reduce ammonia when it's this high is with a 80-90% water change and gravel clean. Then do a 75% water change any day you have an ammonia or nitrite reading above 0ppm, or a nitrate level above 20ppm.

Don't bother testing for nitrates until after the tank has finished cycling because nitrate test kits will read nitrite as nitrate and give you a false reading.

You should also reduce feeding to 2-3 times a week until the tank has cycled. Do a 75% water change and gravel clean 4-8 hours after feeding.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

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Water companies sometimes change their water source and this can cause fluctuations in pH, GH & KH. If your water has no KH (carbonate hardness), then the pH can drop rapidly.

If you add some shells, dead coral rubble, or limestone rock to the tank, it will help neutralise any acids in the water and help stop the pH dropping. You add a small amount and monitor the pH over the next 2 weeks. If it still drops, you add a bit more and monitor for a couple more weeks. Continue adding it until the pH stabilises.

Your livebearers (mollies and platies) don't like acid water (pH below 7.0) and this might be a reason they aren't doing well. They also need a GH (general hardness) around 200ppm for platies, and above 250ppm for mollies.

Having said this, the low pH is actually saving your fish from the ammonia. Ammonia changes into a much more toxic form in water with a pH above 7.0. By having a low pH, the ammonia is in a much less toxic form.

You also don't want to have the pH fluctuating because this harms the fish too.

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If you post pictures of the fish it might offer more information, but at this stage I would say the major issues are ammonia and fluctuating pH. Get these sorted out and the remaining fish should recover.

 

[The Lost Tapes]

Thank you for the reply. Well, the low PH issue is my concern because from my personal experience I have been unable to cycle tanks with a PH around 6.
I did a water change today and that brought the ammonia down to about 3ppm
My water is around 6.6 PH and as for the KH I presume it is low since the PH is low.
I have been dosing Stability daily.
The main issue for me is that I cannot jack the PH up high due to the fish going into shock. Now I know higher PH makes the ammonia more toxic, so I do not know what exactly to do for that. I would say the tank did best with a PH of around 8 from what I saw.
I am afraid of doing daily water changes for the aforementioned PH fluctuations. Would adding crushed coral or something similar to buff the water be a good idea in this case, and if so, where do I put it?
As for removing the carbon, I do not dose medication anymore so I do not think I would need it removed, I am pretty sure all it does is make the water clearer.
Also I have plants in the tank but they are all being killed off rapidly by I presume the bad water parameters. I dose Flourish weekly into the tank as a fertilizer for them.

 

[Colin_T]

Put some shells, limestone or coral rubble in the filter or in the tank as an ornament.

Keep doing daily water changes to get the ammonia level down to 0ppm.