I found this for us NERMS

[tekjunkie28]

https://academic.oup.com/conphys/article/8/1/coz092/5658492

[CT_]

I don't think (I could be wrong?) That people keep pH 4.0 tanks but is it common to have 50+nitrates?

[tekjunkie28]

50+ nitrates is probably like 8/10 tanks tbh. I bet most people who keep fish don't even know to change water until they loose a few fish after a year. Or they clean the tank and just by proxy change some water. 

You can extrapolate from the study that low pH along with high nitrates can cause issues. These issues be not be noticeable to the average person. I would say high nitrates are a bigger issues then what we think. In nature the fish may never see more then 5ppm without human intervention.

Another way to look at it is that from looking at the data is that high nitrates are more detrimental the lower the pH.

[CT_]

The problem I have interpreting this is they don't really establish a high lower bound for the danger zone nitrate or vice versa for pH so yeah 7 is better than 4 pH and 0 nitrates is better than 50 but I can't really say how much is fine according too they're metric.

 

From the data you also can't really see that there's any synergy (in a bad way) between low ph and high nitrate

[tekjunkie28]

True but this study isn't for home fishkeepers. It is more for commerce and environmental use.  That being said there isn't a huge difference in some metrics but enough to show that there is an effect.  The effect is also worse when both are combined. When in nature both would be happening at the same time which is a double whammy to fish.  In a home aquarium then you should already be trying to keep nitrates as low as possible within reason.