Overnight Disaster

[Waterloo Kid]

I woke up this morning and found many of my fish dead and all living ones gasping at the surface. To my knowledge this is what I've lost so far.

Approx 6-8 amano shrimp.
4 tetra (unkown type as they lost all colour)
2 Keyholes
1 Rainbowfish

I expect more to be dead tonight.
Anyway, on discovering the problem I checked temp (26), Ammonia (0), nitrite (0), nitrate (2.5ppm), KH (2) and pH (<6).
It looks like I had a huge pH crash overnight due to CO2 injection and low KH. It must have been very low as I found shrimp (still alive) clinging to the top of the tank walls out of the water. They wouldn't go back in without me physically prodding them. They didn't like that water at all!
I've done a 40% waterchange, stopped CO2 injection, put the lights on to get the plants photosynthesising and added the venturi tube to the powerhead to help drive off CO2. I've collected all the bodies I could find. Not a nice task at all. The remaining fish look to be slightly better (the cockatoos were starting to bicker again) but I do expect to find more bodies when I get home. I'm especially gutted about the Keyholes. They were over 2 years old and were great fish. The tetras were, well, just tetras. You can't tell which ones have died, there are just less of them now. The Keyholes were individuals and will be missed.
I was dosing nitrates to help the plants grow but I'm stopping that until I get a grip with the problem. There is a chance that the KNO3 I was using was not pure but I'd been dosing for 3 weeks. I still think it's a pH crash. While doing the test the liquid turned bright yellow (showing6 or less) even without shaking the test tube. That indicates to me a pH substantially less than 6. After the water change it was showing about 6.2 or so. Normally it's about 6.6 to 6.8
If anyone has read this far and can offer any suggestions as to any other possible causes and remidies then I'd be very grateful.
By the way, my CO2 injection comprises a DIY reactor linked to a single Hagen ladder with the tube set as high as it will go i.e. using only the top third of the ladder.

Ta,

WK

 

[Bloo]

Sorry but can't offer advise (never used CO2 injection and don't fiddle with my pH), though I feel for your loss ! it must be truly awful to wake up and find some many fish dead one morning
I hope you get it sorted and fingers cross no more perish.

 

[CFC]

I beleive your diagnosis is spot on. With a KH that low CO2 can be very dangerous to use without a additional buffer added to stabilise the pH, especially at night when plants stop using CO2 so it just collects in the water rather than being removed.

The first thing to do before restarting your CO2 is raise the buffering capacity of your water, the easiest way to do this is with baking soda added at a teaspoon per gallon to fresh water when you do water changes, its a long process but you are aiming to raise the KH to at least 5 and prefferable 7, adding a small mesh bag with a little crushed coral in it to your external filter will also help.

Next you should always switch off CO2 overnight or switch on a powerhead with a venturi to drive it out of the water while its not being used or it can (as you have found) over saturate and cause a pH crash.

 

[Waterloo Kid]

When I first started dosing CO2 I was paranoid of a pH crash and so measured the pH in the morning and evenign every day for a week or so. I never got more than about a .2 pH swing between lights off and lights on. Guess I ran out of buffering!

WK

 

[Flashfire]

All I have to say is sorry, I've also never used Carbon Dioxide, Rather let the fish make it and the plants also make it at night.

 

[Waterloo Kid]

I'm gettiong a little freaked by this now. Got home yesterday afternoon and you'd never gues anything had been wrong. pH was up to 6.6 and all the remaining fish were absolutely fine. In fact a few were more than fine as they had tucked in to a coupe of shrimp that had died and I'd missed.
Anyway, this morning it was an action replay of yesterday. This time I haven't found any dead fish or shrimp but they were all struggling for breath at the surface. The pH was down to around 6 again. I stopped using CO2 yesterday morning so the only cuse that I can come up with is that the co" being given off by the plants and fish is causing the pH to swing. The buffering capacity must be so low that this is all it takes.
I've upped the aeration and added about 5-10g of bicarbonate of soda to try to stabilise the tank. I didn't have CFC's instructions with me regarding the amount to put in so I only added a bit. I'll be getting some KH additive ASAP. Is the stuff sold commercially just bicarbonate solution? If so I'll take a trip to the shop for some instead of forking out a fortune on label additives.
Can anyone think of any other reason why my pH is all over the place. I know it's the low KH but what is the trigger?

WK

 

[CFC]

What your tank is basicly suffering from is "old tank syndrome" bought on at a accelerated rate by the use of CO2 and the added nitrate which will also acidify water.

As you have realised the buffers in your tank have been used up faster than they have been replaced leaving you with a very pure end product that is easily changable by the factors around it. Your water from the tap naturally has a base pH of 6.6 so when you do a water change this will raise the pH of the aquarium and the small ammount of buffer present will keep it stable for a while. As soon as the lights go out and the plants stop using CO2 and nitrate from the water the ammount of acid producing factors increases which wipes out the remaining buffers and the pH crashes until another water change brings the pH back up. On the whole a very unpleasent enviroment for the fish.

Alkeline raising buffers from the shop are basicly just bicarbonate of soda (baking powder) so in your case where you will be using large ammounts to keep the water stable it would be cheaper to buy from a supermarket .

Use the baking powder at a dose of 1tsp per 5 gallons of water added to the fresh water at water changes NOT added directly to the tank, adding too much at once will cause the pH to sky rocket upwards. Once the KH has stabilised and reads above 3 constantly you can lower the dose to 1/2 tsp to each 5 gallons of water again only added to the fresh water at water changes.

 

[Waterloo Kid]

Interesting, thanks for that.
I was unaware that nitrates can acidify the water. Nitric or nitrous acid I presume?
Tomorrow it's a trip to the lfs to get myself a small quantity of crushed coral. Tonight it's water change time so I'll be adding Bicarb to the new water. When you say 1tsp per gallon is that UK or US gallons? Don't want to get it wrong and mess the fish round again!

On a positive side the wife wanted me to change the tank into a Malawi tank. She's a primary school teacher and so likes bright colours, especially yellow. With water like mine there's no way that's an option! I'd be using bicarb by the tonne!

WK

Edit:
Would you suggest that 3 large (approx 40%) water changes over the weekend be done to try to 'reset' the tank. It's been gong well for over 3 years until this happened so the balance must be only very slightly out.

 

[CFC]

Sorry i did mean US gallons, should have been clearer on that. If its easier 1 US gallon is equal to around 10 litres of water.

Lucky escape on the Malaiwi's!! nasty little things.

 

[Waterloo Kid]

LOL, My thoughts exactly!
Makes it easier then as my water change buckets are 10 litres each!

WK

 

[iggy01]

Please be careful when adding bicarbonate of soda. 1 tsp will raise the KH of 50 litres of water by 4dH. The bottom of this page gives a good explanation.

Good luck!

 

[SarahBravo]

Sorry, isn't one US gallon about 4 litres?? Lemme check.... yep, just under 4 litres.

 

[Discomafia]

3.78 litres to be precise...