Diamond tetras again... I give up...

[BigBen]

Little and often I would say. I've increased the water changes in my Cory tank but I'm still doing the same amount throughout the week, about 25% of the tanks volume.

[Lee_k]

What is it that causes the PH to keep change over time like that? - I cant imagine thats ever going to be great as i'd always read a constant (even if not perfect for the fish) is better than the yoyo'ing effect of trying to correct

[BigBen]

What is it that causes the PH to keep change over time like that? - I cant imagine thats ever going to be great as i'd always read a constant (even if not perfect for the fish) is better than the yoyo'ing effect of trying to correct

Low KH allows the pH to swing. Where we are the water goes incredibly soft through the winter but increases a little through the summer. I've never had a massive issue with it with my fish to be honest, but I think WR has a more sensitive species by the sounds of it.

[Suse]

So I'm sorry to be so stupid... This is the equivalent of my thinking out loud.

Should I only be doing small water changes a week then rather than around the 50% mark, which I've always thought of as the golden rule? By doing the small water change I assume the pH stays lower all the time than swinging up and falling? Which is then more stable for the fish?

If the pH drops over a period of time - as per BigBen's post - do I need to see what the tank is at and then try and match it with water that's been left out?

Does the volume of water in the tank make a difference?

I tested all the tanks last night. The 190 has dropped from the previous deep blue - it's due a water change tomorrow.

This is the 190 from last night (water change last Weds):



And this is the diamond tank after a 50% water change on Sunday :



?

It's the lack of KH aka carbonate hardness that makes the pH drop. There are no carbonates to mop up the excess acid produced by natural processes in the tank (fish respiration, excretion, organic matter decay etc). Once the carbonates are used up, pH drops off a cliff.

I have the same issue in my tank with very low KH. The fish I keep are sturdy and don't seem to be bothered by it. Some are. Your diamonds may well be.

A very easy fix is to get some potassium bicarbonate (a few quid off eBay) and then add it to your tank with the water change every week. As a rough and ready estimate, 1 level teaspoon raises the KH in 100 litres of water by 3 degrees. You need about 4-5 degrees of KH to be sure of pH stability.

Work out what you need and make a solution up for the full water change. Then add a bit to each bucket if using buckets, or put in a bit every few mins if using a hose to refill.

I got mine from this supplier:

https://www.ebay.co.uk/itm/POTASSIUM-BI ... Sw1QpZ~Fv5

I now use a cuttlebone in my filter instead so I don't have to remember to add during water changes, but this is less reliable.

[WinterRose73]

Thanks again everyone. I'll be honest and say that although I regularly test the three main things it had never ever occurred to me to look at the pH in the tanks. Not once.

One last thing, what is it that I am aiming for the pH to actually be? When I'm testing the tank water what sort of number / range am I looking for? If diamonds can sit between 6-7 does it matter as long as it's between those numbers?

I feel awful if it is this stupidity that has caused the loss of those poor, poor diamonds but lesson learned....

[Suse]

The pH is not the important thing, the stability is. Anywhere from 6-7.4 ish is fine for most tetras. The problem is the big sudden swings, which increasing KH will stop.

This is not necessarily the cause of the deaths. It could still be eg a latent illness. But in the absence of any other clear factor to address, it's definitely worth fixing.

[BigBen]

You shouldn't be hard on yourself here. Why would anyone know their water changes a bit seasonally? I would imagine they are also weak stock to be honest, I've never had such issues with dies offs like this and I noticed a seasonal change in pH years ago. I've never done much about it even knowing about it.

[WinterRose73]

So have to say I'm confused. Last night I tested the pH in the diamond tank and it was as below :



I have just tested again and the colour is darker:



The only change between these tests is the addition of two cattapa leaves. Would that be enough to bring the pH up?

[SPACKlick]

Catappa leaves lower pH don't they?#

I've never seen my API pH be that blue...Did you shake it up properly?

[WinterRose73]

Catappa leaves lower pH don't they?#

I've never seen my API pH be that blue...Did you shake it up properly?

OK, please totally ignore the blue test - no idea at all what I did to get that colour!!!

Just done it again and we're back to the very pale green, similar to before the water change.