HELP water change killed all my fish!!

Hi all

I refer back to this post I made a couple of days ago for background:


I did about a 65/70% water change a few hours using remineralised RO water, I just went back to feed the tank and my fish were all lethargic/dead. I quickly grabbed the first thing to hand, a 1 litre jug and scooped some water out of my other tank which hasn't been changed today. I scooped up everything I could to try and save them but have lost most of my tank inhabitants.

I tested the water (see pic) - I was aware of the ammonia issue, that's what I was trying to sort based on the previous thread. But the pH!!!! I don't understand why it is so high! Has that killed my fish? I didn't add anything to raise the pH, in fact I always put a tiny amount of pH lowerer in as my hardscape tends to raise it to about 7.4 anyway.

I'm currently draining the tank completely but I don't know what to do! I can't leave the fish in this litre jug for long. I have a 25 litre bottle of RO water that I'm about to test, if that's OK I will use that for now but I just don't understand what's happened and why they've all died. I'm absolutely gutted that I couldn't save more.

Lcc86 said:

using remineralised RO water

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Is this water you remineralised yourself or did you buy it remineralised? If it's the latter, was it prepared to use for Rift Lake cichlids, which would mean made very hard and with high pH?

Essjay said:

Is this water you remineralised yourself or did you buy it remineralised? If it's the latter, was it prepared to use for Rift Lake cichlids, which would mean made very hard and with high pH?

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@Essjay No I prepared it myself. There's only a couple of scenarios I can think of -

1. Problem at the RO facility (unlikely)
2. I've accidentally added alkaline buffer instead of acid buffer and increased the pH
3. Problem with the container I'm using, but these containers never have chemicals in them to my knowledge as my partner uses RO water for work

I tested the bottle of RO water that I have left (see pic) so am going to add this now and put the fish back. I've emptied the old water out completely.

I didn't get any pics of the fish before I scooped them out but they looked fuzzy, and had cloudy eyes too. The frogs seem to have tolerated it better but I've also lost my shrimp. I found one live cory as I was emptying the tank but several dead ones. I'll upload some pics of the dead fish shortly.

I've put the RO water from my second post in the tank, put the survivors back in and the cories are all extremely lethargic again. I've again taken a litre of water out of my 6gal and scooped them all out and now they're fine. I don't understand what's going on, nothing else has gone into this tank today to cause this - no wood, rocks, no changes other than the bad water which I've removed.

I've got no more RO water left so will go and get some now but I'm not sure what to do, I can't keep them in a 1 litre jug and I definitely can't put them in the betta tank with the water that is OK because the betta is way too aggressive.

Do they just need time to recover in their tank? They go lethargic straight away with clamped fins, breathing seems OK but they just don't look right so I didn't want to leave them there.

I have a quarantine tank in the basement I can grab and set up with my current filter to see if that helps. That's my last hope.

Sh** sorry to hear this. What a nightmare. If the pH is 8.4 as indicated in your pictures then that ammonia reading you posted in the other thread would have been very toxic to the fish. I think your ammonia reading was about 3.0 ppm ?

@TwoTankAmin will now. Maybe he can confirm. I think the difference in toxicity / lethality with your high ammonia and a pH of 7.4 ish and 8.4 ish is significant. Life or death perhaps.

I don't know anything about remineralising RO. What did you use?

Could be a sad perfect storm here. Root tabs causing an ammonia spike and reminersaling causing a high pH spike. The higher the pH the more dangerous ammonia is for fish. Ammonia as we know it from our test readings.

Ammonia exists in two forms in water: un-ionized ammonia (NH3+) and ionized ammonium (NH4+). The ratio between these two forms is determined by the water's pH level.

At higher pH levels (more alkaline conditions), more ammonia exists in the toxic un-ionized form (NH3+), which can easily penetrate fish gills and disrupt their internal functions.

Lcc86 said:

@Essjay No I prepared it myself. There's only a couple of scenarios I can think of -

1. Problem at the RO facility (unlikely)
2. I've accidentally added alkaline buffer instead of acid buffer and increased the pH
3. Problem with the container I'm using, but these containers never have chemicals in them to my knowledge as my partner uses RO water for work

I tested the bottle of RO water that I have left (see pic) so am going to add this now and put the fish back. I've emptied the old water out completely.

I didn't get any pics of the fish before I scooped them out but they looked fuzzy, and had cloudy eyes too. The frogs seem to have tolerated it better but I've also lost my shrimp. I found one live cory as I was emptying the tank but several dead ones. I'll upload some pics of the dead fish shortly.

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Is that picture you posted the straight RO water readings? Because the pH is showing as acidic? Might be nothing. The other readings if that's straight RO are good

The RO water before you add anything should be that turquoise colour on the chart. Bang on 7.0. I use RO and the same test kit. This might not be relevant.

AJ356 said:

Sh** sorry to hear this. What a nightmare. If the pH is 8.4 as indicated in your pictures then that ammonia reading you posted in the other thread would have been very toxic to the fish. I think your ammonia reading was about 3.0 ppm ?

@TwoTankAmin will now. Maybe he can confirm. I think the difference in toxicity / lethality with your high ammonia and a pH of 7.4 ish and 8.4 ish is significant. Life or death perhaps.

I don't know anything about remineralising RO. What did you use?

Could be a sad perfect storm here. Root tabs causing an ammonia spike and reminersaling causing a high pH spike. The higher the pH the more dangerous ammonia is for fish. Ammonia as we know it from our test readings.

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I think you're right, I just don't know what caused the spike in pH. I think it must've been my mistake, that's the only explanation.

I use seachem equilibrium to remineralise.

AJ356 said:

Is that picture you posted the straight RO water readings? Because the pH is showing as acidic? Might be nothing. The other readings if that's straight RO are good

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That was RO water where I'd added a little seachem buffer just to reduce pH slightly, it hadn't gone in the tank at that point.

AJ356 said:

The RO water before you add anything should be that turquoise colour on the chart. Bang on 7.0. I use RO and the same test kit. This might not be relevant.

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Thanks, I didn't test before I added the buffer but I'm sure it would've been 7 as there's no reason for it not to have been.

With surviving Fish maybe just extra airpump for surface agitation / max oxygen

gwand said:

Ammonia exists in two forms in water: un-ionized ammonia (NH3+) and ionized ammonium (NH4+). The ratio between these two forms is determined by the water's pH level.

At higher pH levels (more alkaline conditions), more ammonia exists in the toxic un-ionized form (NH3+), which can easily penetrate fish gills and disrupt their internal functions.

Click to expand...

I never knew this until today. Always something to learn in this hobby but wish it hadn't been such a painful lesson to learn.

I grabbed my QT tank from the basement and set it up, went and got some more RO water and have put the fish in, I lost one before I had finished setting up. I'm down to one panda cory, my three original julii's and my three ADF's. Basically killed every fish that I'd bought this past 12 months. Gutted.

@Essjay will know. I wonder if the Seachem product increases the KH, because with straight RO the KH is zero which makes buffer products real risky for pH swings. I don't think that happened, but worth knowing.

Got some pics of some of the fish that I couldn't save.

I've left the remaining fish in the QT tank to hopefully recover, I'm not confident they will all make it. It's night time here now so I can't keep messing with things.

I'll test the water in the main tank in the morning and post results.