Science literature: pH makes a difference with nitrates

[neutrino]

Genuine aquatic science, not some guy who fancies himself as the father of all fish keepers or a guy with a blog who fancies himself to be a science authority. And while I'm always for keeping nitrates as low as you reasonably can, consider how this accounts for (some of) the varying opinions (and results) regarding nitrate levels-- and why some fish may seem to be more sensitive than others.

Simultaneous exposure to nitrate and low pH reduces the blood oxygen-carrying capacity and functional performance of a freshwater fish | Conservation Physiology | Oxford Academic (oup.com)

 

[RD.]

Great read, thanks for posting!

 

[duanes]

Great info posted in the above study
One of the things I found fascinating about it, is how quickly the lower oxygen levels caused by high nitrate, negatively affected the fish, at an aberrant pH (a matter of weeks depending on nitrate levels).
And although this study was about quickly dropping pH, on the hardy variable parameter tolerant Australian Perch (6.5 to 8.2).
I would also extrapolate that the same thing could happen when low pH evolved type fish were held in high pH water.
If so,......it's no wonder the immune response of oscars and other S American soft water species put in the usual N American higher pH tap water succumb to chronic disease like HITH in that situation, and how bacteria that thrive in higher pH water would take advantage of the soft water species lack of immunity to those bacteria.

 

[RD.]

I would also extrapolate that the same thing could happen when low pH evolved type fish were held in high pH water.
If so,......it's no wonder the immune response of oscars and other S American soft water species put in the usual N American higher pH tap water succumb to chronic disease like HITH in that situation, and how bacteria that thrive in higher pH water would take advantage of the soft water species lack of immunity to those bacteria.

....... but again, that becomes a case of operator error, as much or more than the tap water parameters. Keep the DOC's and overall bacteria count low, along with all other potential stressors, and in many cases pH is no longer an issue. I feel like a broken record, but this is precisely why some folks have zero issues with various HITH prone species such as Oscars, and others can't seem to avoid the pits & holes. Some of that could simply be individual immune systems with each fish, but IME it almost always leads back to someone that has stress in their tank and isn't experienced enough to see the signs. This goes far beyond pH values.

In another recent thread someone that currently has HITH head in some of their SA fish (species myself & many others have kept successfully for years in pH 8.0) stated; "I run a drip system so water change shouldn’t be an issue. " A continuous drip does not necessarily = low nitrates. Depending on the drip rate, and the bio load of their tank, a large once a week water change could potentially be far better at keeping nitrates (bacteria/waste) lower in their system, compared to a continuous drip.

A lot of this is common sense, or at least should be, but it's good to see some actual science to explain how various combinations of stressors can affect the health of a fish, even during a fairly short duration of time.

 

[duanes]

I agree, and use nitrate as indicator, of all the other components we don't and can't normally have the ability to test for like DOC under average aquarium norms.
And agree, although a drip system might sound good on the surface.
If the drip is too slow, without moving enough volume, nutrients are not only "not" replaced with non-nutrient water, they can be less effective than normal water changes.
I like to change over 100% of a tanks water per week, but even that does not compare to what happens in nature, and I sometimes feel like a slacker
This study seems to prove that high nitrate slows the uptake of oxygen for fish, so is just another indicator what many aquarists consider acceptable, is really not.

 

[neutrino]

Imo the study helps explain some things. My thoughts extrapolated from the article:

1. May help explain why people keeping blackwater fish in low pH tanks find they need to also keep nitrates low for fish to stay healthy. I'm NOT saying this is the only factor or that it takes other sensible things out of the picture, such as the need for very clean water, low bacteria load, and the apparent benefits of tannins.

2. Might (help) explain why it seems you can get away with higher nitrates with something like African cichlids, typically kept in hard water, higher pH tanks. I used to know (through a forum) a guy who for several years was highly regarded as a Cyphotilapia breeder in Australia. Due to water restrictions he waited for nitrates to hit 50 before doing his water changes, yet his fish were quite healthy and his tanks were immaculate.

So I think a few things here. First of all ignore whoever tries to tell you high nitrates do not affect your fish, don't like to say this but it's hard for me not to consider them idiots-- or maybe contrarians out to prove a point, which occasionally amounts to the same thing. Second, what's "high" for nitrates depends on a few things. You can't blissfully keep Malawi cichlids in pH 8 and nitrates over 40 (which might be okay when everything else is in order), think you've got this aquarist thing whipped, and try doing the same with S. Daemon. On the other hand, if you find your soft water, pH 5.5 Satanoperca tank has issues when nitrates go over 10, don't make 10 the cosmic limit for everyone else's tank.

As for the pH thing, I find it varies, but-- based on the loads of empirical evidence, for many species it's clearly not necessary to replicate what we believe to be their native pH or hardness. I emphasize believe to be because I see a lot of mistaken assumptions out there (e.g. discus all come from very soft. very warm, low pH water-- some do, others don't), and because the main river we may associate to a species isn't always the smaller tributary from which it's collected, where pH and hardness may be quite different. And species simply vary in adaptability and the range they can comfortably handle (why can't people get this through their heads). I have some wild A. metae from Rio Atabapo, typically black water fish. I've moved them around from tank to tank a good bit and they could care less about pH or hardness (up to 8, anyway). I had wild Heros sp. rotkeil, same thing. Same with the Geo pyrocephalus I bred for at least a dozen years. On the other hand I had some Guianacara that could not handle high pH. Some are more adaptable than others and ime it clearly varies by species...

I've mentioned this Amazonas magazine article on breeding Geo mirabilis before, read it back when, can only find a partial reproduction lately, but here's his parameters: TDS 480, GH 340, KH 100 (as close as I can make out), nitrates "under 40 ppm," pH 8.3. Not what I'd do but there it is 'in black and white.'
https://www.amazonasmagazine.com/2017/07/13/amazonas-video-bonus-breeding-geophagus-mirabilis/

duanes -- I like to do large water changes and I agree with a lot of what you're saying, but assuming good filtration (also feeding sensibly, not overstocking, etc.) my thing is there's not a good comparison for water changes needed vs. river flow, etc. Which is fortunate, otherwise we'd all be in trouble. I have my own sweet spot for my tanks, often do more than that, but with SO many variables I don't like to get too specific making recommendations.