Losing Gouramis & Cordydora

[liv_2025]

New Here! Asking for help but please be kind! I have been in the fish hobby for over a decade so I am not a beginner but have been dealing with fish dying and I not 100% sure why

I have a 20gal heavily planted aquarium that's been running since mid 2023.
It's a community tank containing a small amount of endlers, platies, mollies. (The platies and mollies are babies growing up and I will likely end up rehoming most of them).
1 Hillstream Loach and now 3 Corydoras(yes I had 6 but have lost 2 way back when I added them in and yesterday my 3rd was having issues)
I only have 1 honey gourami left(I ordered online Jan and had to get 6, I was planning to rehome a few of them)

I am very aware of not overstocking, and that's the least of worries right now. I have double filtration with a power filter and 2 sponge filters. Everyone has been doing fantastic since this tank was started, until the end of Jan of this year.

I started losing the honey gourami and couldn't figure out why. Overnight they took a turn, I woke up to one laying on the bottom and when it would swim, it would swim upside down/spin.
I tried getting it in quarantine with medication ASAP, but it didn't survive. The next few days 2 more were already gone. I had 3 left were doing good for a few days and than I noticed 1 had clamped fins so went ahead and put them all in quarantine with medication and 2 died overnight the last one was acting normal, he is back in the main tank.

Of course I checked my parameters and everything was normal.
PH was around 7.6
Temp: is 77-78F
Ammonia- 0
Nitrite-0
Nitrate- 0 (which is normal as my tank is fully planted, after an hr the result was a bit more orange closer to 5 if that makes a difference)

Last night I noticed 1 of my Corydoras doing the samething, swimming upside down. I am looking for it, but it's likely passed underneath the wood decor in my tank.

Every other fish including the other Corydoras are acting completely normal.

Checked my parameters again no difference.

I do have a GH & KH test kit too, which I was to check. And I think this is my issue

My home does have a water softener, so my water is very soft.

KH: 15dkh(268.5ppm)
GH: 2-3dgh(35.8-53.7ppm)
*Plants are growing very well too, with added fertilizer

Of course these levels are not good for any fish that I have from what I am seeing, but would my fish just adapt to these than since their hardy?
Over the years and now I have never had issues with keeping live-bearers, betta's, snails etc.
The endlers I have had for 3 years.

I have had the Corydoras since the beginning of Dec.
Did the gouramis and Corydoras pass because their more sensitive? If so wouldn't they have passed shortly after I got them?
*First time keeping Corydoras

I was told the better option would be to start adding a % of RO mixed with my tap to balance it out and get the reading I need. But to do this slowly to not effect the rest of the fish.

My question is should I, even though I could stress or kill the healthy fish I have now or go ahead and start working on adding RO slowly?

I used to use RO a few years back but it's such a pain to fill up large tanks, I haven't had any issues using tap so I didn't think anything of it.

Any kind feedback is appreciated

 

[Aiken Drum]

Water softeners work on an ion exchange principal. What this does is it removes the calcium and magnesium ions that gives the water general hardness, and replaces them with sodium ions that doesnt effect GH.

Sodium in general is not good for freshwater fish. Sometimes people get away with it, sometimes they don't. There are 2 factors here, how hard is the water before it goes through the softener, and what species you keep.

If you have particularly hard water, then that's a lot of calcium and magnesium being removed, and therefore a lot of sodium going back in.

Fish that prefer harder water are going to be more tolerant to sodium than fish that prefer softer water. So in your case the livebearers are hard water fish and more tolerant to sodium, whereas the gourami are soft water fish and less tolerant to sodium. Corys really depends on the specific species.

I think the issue is your water softener rather than the waters GH.

There are options, but really, you should match the fish to your water. So in your case stick to harder water fish.

Water softeners come with a bypass, so you could try and use water for your water changes that hasn't gone through the softener, and doesn't contain the sodium. The soft water fish are going to be more tolerant to high calcium and magnesium than they are to sodium, but its still not ideal for them.

You could go the RO route you suggest. Mixing RO water with your softened water would reduce the amount of sodium. Mixing with bypassed unsoftened water would lower the hardness without the sodium going in. Or go 100% RO and remineralise using buffering salts to the parameters you want.

You could change the resin in the softener to one that uses potassium instead of sodium.

If you go down any of these routes, make sure you gradually change the water as you dont want the mineral content changing too quickly as fish don't like that.

But really, getting the water right for soft water fish will result in it not being right for the hard water fish, and trying for a compromise isn't right for either end of the spectrum, but they would probably be ok.

 

[liv_2025]

Thank you for your kind reply!

So I was just now told are outside spickets do not go through the softener.
They're currently not on because of winter.

What do you think would be the better option, using a percentage of RO or switching to the water that hasn't gone through the softener? Start with 10% or go lower?
Water is from a well, if that's a difference.

My only concern is that my family turns them off during winter so they'd only be available from spring to fall. During winter could I exchange for RO when doing water changes or would that completely mess up everything?

Sorry for all the questions just want to get this right

 

[liv_2025]

So the outside water that doesn't go through the softer goes through an iron filter. Is that a good thing?

 

[Aiken Drum]

There should be a bypass on the pipework adjacent to the actual softener, so you can turn it off for your water changes, run enough water to clear the softened water from the pipework, and then turn the bypass back off again so softened water again water comes out of your tap. Something like this.


The best option is to just keep the livebearers, as they are tolerant of the mineral content regardless of whether its sodium calcium or magnesium.

If you are set on keeping the soft water fish, and didn't want to go down the 100% RO and remineralise, you could just see how things go bypassing the softener and see how just omitting the sodium goes. I would use the unsoftened water though, and see what mix gets you to a GH of around 8 to 10. What that mix is would depend on the GH of your unsoftened water. Assuming your GH and KH are similar, then that would be about 50/50 mix. So you could do a 10% water change using RO every couple of days until your mix is where you want it, then mix with your tap water you to keep it there. Gradually the sodium will be changed out.

I honestly have no real idea about the iron filter. If i had to hazard a guess I don't think it will effect the fish. Plants need iron though, but that's probably picked up by your ferts.

 

[liv_2025]

So it sounds like I do have the bypass option! Will try that out.

Should I start removing 10% of the current water every other day or like once a week to replace with the water i need? I don't want to remove to much water at a time.

I will test out the bypassed water and see what it is when I get the chance.

 

[Aiken Drum]

A 10% water change once a week is hardly worth doing. Thinking about it, what i would do is the 10% water change every 2 days, but alternate between a RO water change and unsoftened tapwater water change. This will gradually lower the sodium content and raise the GH. You can monitor the effects on your fish over a couple of weeks and report back if this reaction is adverse. Once you are where you want to be parameter wise, maybe after a couple of weeks, do bigger, less frequent water changes with your RO/ unsoftened tapwater mix.

 

[liv_2025]

Awesome thanks!