Whole house water filter killing my tetra?

[Jimfish98]

Have had my tank up and running for some time and no new fish for months. System was running smooth until I got a whole house water filtration system. Goes through a sediment filter and a carbon filter, then an alternative water softener. There is no salt use in the softener. Did a water change and noticed a massive die off in tetra, about 15 in a few days. I am losing up to 5 a week now. My Danio, Barbs, Pleco, Mollies, Snails, and Goldfish all seem to be completely normal with no loss. 

Are tetra that sensitive that they would die off so rapidly? Did I strip too much out of the water and need mineral replacement? At a loss figuring this one out. 

[nabokovfan87]

Can you post testing results of you tank as well as your tapwater?
1. Take a sample from the tank, test it.
2. Take a sample from the tap, test it.
3. Take that same sample from the tap, aerate it for 24 hours with an airstone, then re-test.

My gut assumption is that you're seeing PH swings, potentially very soft water compared to what the fish are used to.

[Chick-In-Of-TheSea]

If your water is soft you can consider adding crushed coral to the tank.

[lefty o]

what is the alternative water softener? is it putting something in the water?

[Jimfish98]

On 5/28/2022 at 5:22 PM, nabokovfan87 said:

Can you post testing results of you tank as well as your tapwater?
1. Take a sample from the tank, test it.
2. Take a sample from the tap, test it.
3. Take that same sample from the tap, aerate it for 24 hours with an airstone, then re-test.

My gut assumption is that you're seeing PH swings, potentially very soft water compared to what the fish are used to.

No changes in my normal testing, but it got me thinking what do I not normally test for and found the solution I think.

[Jimfish98]

On 5/28/2022 at 7:16 PM, lefty o said:

what is the alternative water softener? is it putting something in the water?

You nailed it I think. After Nabo's response I pulled out my phosphate test kit as I have never really had to use it. I am somewhere between 5 and 10 ppm. Tested the water out of where I fill the tank, at 1ppm. Filled up the test kit from the hose before the filter, 0ppm. Large water change brought the tank to 1ppm likely and the ATO has been pumping in 1ppm to replace evaporated water, likely pushing the PPM higher and higher. Added a giant bag of GFO and will check it out in the morning. If it drops, will have to build a bypass on the water filter to turn off for filling up the ATO and doing water changes. 

[nabokovfan87]

On 5/28/2022 at 4:28 PM, Jimfish98 said:

You nailed it I think. After Nabo's response I pulled out my phosphate test kit as I have never really had to use it. I am somewhere between 5 and 10 ppm. Tested the water out of where I fill the tank, at 1ppm. Filled up the test kit from the hose before the filter, 0ppm. Large water change brought the tank to 1ppm likely and the ATO has been pumping in 1ppm to replace evaporated water, likely pushing the PPM higher and higher. Added a giant bag of GFO and will check it out in the morning. If it drops, will have to build a bypass on the water filter to turn off for filling up the ATO and doing water changes. 

Oh this is interesting!  I would be intrigued to know if this is the full result.  A lot of people around where I live tend to get sold a system similar to what you have been describing.  I'm more of the mindset of just a good series of filters that go to whatever need be (ATO style, under sink drinking filter, but the whole house version).  I do see the advantage of re-mineralizing water, don't really hate hard water (the pipes do, but me no) as long as it's stuff my body actually needs and not weird stuff.

There was an episode of Clarkson's farm on water testing, pretty funny stuff there too.