Neon Tetras dying fast, but nothing else is

[Blaha]

I'm confused.
I have had a bit of an algae bloom for a couple weeks and my Cory's seemed stressed. It's getting better, they are calming a bit, but now my school of 7 Neon Tetras is dying. 1 yesterday. 1 and hour ago, and another is having troubles swimming now, and it's stripe is not really visible.
My other tank mates seem fine though, I think. The 6 Black Neons seem pretty much fine. The 2 Emerald Corys are calming down, but not fully relaxed. I never am able to find all 6 Kuhli's at any one time but I haven't seen any deaths or signs of problems when they are swimming about. 2 of the Hillstreams are always visible and kind of near each other, the 3rd hasn't been seen in a few days, alive or dead, and there's very few places it could be where the current couldn't move it if it died. Everything in the tank has been there for over 2 months, except 2 of the hillstreams which were added about 10 days ago, and were treated for possible disease.

I've had fish on and off for several years and either everything is great or everything dies all at once and I don't want that to happen again because I just got this iteration established and cycled and whatnot

So long story short: Lot's of algae, 85% of my fish are doing good, and specifically the Neon Tertras are droping like dominos.
It's a 29 Gallon with a spongefilter and powerhead from the Co-op , and a fluval light.
Parameters
78 degrees. Over the course of a few months I've raised and lowered the heater temp, and even turned it off, and it's always 76-78
0 Ammonia and Chlorine
6.8-7.6 pH, I struggle to discern the shades
80KH 150-300 KH
0 Nitrite
50-100 Nitrate. I do 1-2 10-15% changes per week and it is rarely lower than 50 and never higher than 100. Not great but it's been consistently there for a while.
Nothing else has rapidly changed. I had the powerhead on for a longer than having these fish in a different spot, but turned it off for about a week because it seemed like too much current on my Tiger Lotus causing it to shed leaves about as quick as they sprouted. I then moved it there and turned it back on a couple days ago

[igalysh]

Is your water cloudy? The picture seems to show cloudy water. You may need to improve your filtration. I have a tank with a sponge filter and improved my water by connecting the power head to the sponge filter. It improves the efficiency of the sponge filter. I also tried out the fluidized bed filter and that also improved the clarity of the water.

You may want to read this: https://aquariumscience.org/index.php/4-3-free-floating-bacteria/

I found the website quite useful and added more filtration capacity which cleared up the water in all my tanks. You may have a high amounts of bacteria free floating in the water which stresses the fish's immune system.

Ivan

[Brandy]

Your water is hard and your nitrates are high. Ideally you will lower both of those things for neons...test tap water, and check that it is not full of nitrates at the tap. If it is not you should change water to lower your nitrates.

If your tap water IS full of nitrates, then you probably want to add some plants, such as pothos or floating plants, that will use it up for you, or you want to use some distilled water or rainwater to change the water.

[HH Morant]

igalysh is right about filtration. It is not a quick fix, but aquariumscience.org changed my approach to filtration. It works.

In the short run, you might try to cut back on feeding. Overfeeding often increases bad bacteria in aquarium water, causing the water to be cloudy. Bad bacteria in the water can overcome the immune system of the fish.

I have the urge to overfeed, and I think most people do. The fish act as if they are starving even immediately after feeding. But they are not starving. They are actually fine. Measuring the food each day is a good way to limit overfeeding. I also have a fasting day every week, when I don't feed the fish.

 

[Colu]

High levels of nitrates can affect a fish immune system I would try get it to about 20ppm with increase water changes @Brandy suggested  if you have high levels of nirates in your tap water I would add seachems matrix to your filter to help remove the nirates I think thats most likely the cause of your problems I would also add an extra air stone

Edited October 30, 2021 by Colu

[Blaha]

Thank you everyone,

The water is a little cloudy. It was worse until I turned the powerhead back on. My phone is also 7 years old and the plastic over the lens is starting to get too scuffed so it makes it look cloudier than it is

My filtration is the Large size sponge filter and I have a pre-filter sponge on the powerhead intake.

I've tested my tap before and it has low to no nitrates if I'm remembering correctly. The tap is just that hard, and believe it or not my old house used to have even harder water. Like a few times a year every faucet/showerhead had to be removed and soaked in a de-calcifier for a day because it was hurting water flow. This water didn't seem that hard to me by comparison.

I will check out this link and look into increasing water changes. I am nervous to do too many water changes by either frequency or volume and hurt the fish that way. I have lots of plants, they are just young and need some time to grow.

Something that was really cool is I got a Tiger Lotus Blulb and after a few days, during the time I was expecting some melting back, half the bulb broke off and since it still had leaves I decided to keep it in to see what happened. It ended up taking root and both of them are now starting to shoot out leaves quickly. In a little while those alone should massively increase my plant volume

 

[igalysh]

From the same website, https://aquariumscience.org/index.php/17-aquarium-fish-selection/

If you scroll down a ways, there is discussion on neon tetras. The website states they don't do well in water with a lot of free floating bacteria. I didn't know they were blackwater fish.

Ivan

[Blaha]

There was a part in the first link that mentioned the river they come from is ph 4.5-6 and that it's so soft most aquarium couldnt survive there because the water would pull the salt out of their bodies through their gills.

That's nuts. I knew that calling them fragile was a myth but wow, that's some scary environment. Being in that water for a while would probably even start to harm outer layers of human skin

[Colu]

On 10/30/2021 at 2:25 AM, igalysh said:

didn't know they were blackwater fish.

Ivan

They have been bred for aquarium trade since the 1930s so they have adapted to a wide range of water conditions