Looks like a leopard ctenopoma which should be fine with fish that size.Is that a Climbing Perch I can see in the pic? That's another fish that can get aggressive and injure or harrass other fish.
I think microbial nitrification will be reduced at lower pH, but it definitely won't stop.Please be aware that a pH crash can kill off the beneficial bacteria in your filter. Nitrifying bacteria reproduction reduces at around pH 6 and they die if the pH gets as low as 5.5.
I would skip the testing, frequent 50%+ WC short term the 50% weekly, remove the waste and reset tank weekly
Little if nothing to be gain.
1. Test kit unreliable and prone to user error and poor interpretation, esp when we not doing them on a regular basis
3. Will the result change the treatment? subject to point 1. & 2.
4. Do you have the right test kit handy, if not with lockdown it will be a few days
5. When have a basic history and a Biweekly 35% WC in high tech tank is the obvious main culprit ATM (accumulation of salts and toxics etc)
So IMO Testing is waste of time in this case as it wont change anything esp shot term. Treat the obvious
I’m sorry Zeus but I too, don’t agree with this at all. I don’t think being dismissive of the potential value of the information a water test may yield is helpful here
User error is unlikely if the tester follows the simple step by step instructions on the box, which for most people is not a difficult task. I always repeat the test twice or even three times, to ensure that there is no error.
The accuracy of home test kits is a much discussed subject on this forum, not so much of late but certainly two or three years ago, test kits were possibly the most debated theme outside of lighting and C02!
To be honest I never really absorbed the scientific reasons given but accepted the facts due to the facts being offered, were backed by very confident and experienced people.
As I remember it, most hobby kits are capable of measuring within reasonable limits but are often influenced by other chemicals that might be present in a aquarium.
Or in other words (maybe?) if you had a bucket of pure RO water and added a single element then that element might be detected quite accurately by the test kit but if you then added several other chemicals then the test results might well be effected and become inaccurate?
I am really not sure if that is a good analogy, maybe someone with a better grasp can explain it better.
I also feel that just resolving the issue with water changes, without even bothering to try and identify what the cause of the issue is, guarantees no long term experience value for the OP either.
In order to reduce the likelihood of a pH crash, your best bet may be to keep CO2 off for a while or reduce injection rate. Dimming your tank lighting should help as it will reduce the rate of CO2 usage by your plants.
So, although your measurement clearly shows a pH of 6.6, it could have dropped to a much lower figure whilst CO2 was being injected. How this may have affected your specific fish I don't know but it is possibly worthy of further investigation.
Thanks for your comments @jaypeecee.
I turned the CO2 back off and dimmed the lights as soon as you'd said, and it's still off at the moment. My lighting fades in from 12-2pm, and fades out from 9-11pm. I took the latest reading around 2pm so I'll take another Round 10pm tonight.
I will look into the needs of the fish that died in more detail. I didn't think Congo's were particularly sensitive, but have since read that they can be.
What KH should I be aiming for in mg/l?
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