KH is OK, but PH is waaaayyyy low...help?!?
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Old 06-26-2003, 05:20 PM   #1
29gallonsteve
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Hopefully, someone can shed some light on the phosphate/KH/pH relationship for me...(assuming there is one).

Moderately planted tank with heavier fish load:

29g freshwater
MgSO4 - dosing at 0.8ppm/ml daily
K2SO4 - 1/4 tsp at 25% water change (weekly)
pH - 6.0-6.4
KH - 5.5 dKH
GH - 14 dGH
CO2 - DIY injected with gravel vac
PO4 - 0.5-1.0
NO3 - 10ppm

I am also dosing Seachem Iron and Flourish 2-3 times/week @ 1.5 ml per dose.

Feeding fish moderately every-other day.

Why is my pH so low? Considering no other factors other than CO2/pH/KH, my CO2 concentration is approx 93+ppm...

My fish display no signs of toxcicity, breathing or stress. As a matter of fact, the other day I think I caught my two gold barbs working on a mating ritual!

My test kits are fine...my 'out of tap' for pH is 7.0+ (didn't test PO4 or KH/GH of tap - guess I should).

Any help or advice? Is my PO4 level (with some other nutrient missing) causing a drop in PH???

I have had crypt melt lately (tried to transplant some of them) and recently jacked up my co2 production (I use standard mix instead of Jello)...but nothing added to the tank that could contribute to shift (that I can think of).

Almost forgot to mention that I have very light filtration Penguin 125 with sponge filter material blocking the outlet (to prevent surface agitation).

Since I slowed my filtration down, would the carbonic acid created by degrading fish waste cause my ph to go more acidic???

Thanks,
Steve
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Old 06-27-2003, 01:06 PM   #2
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I racked my brain...hard...

For the sake of simplicity...I tested my tap water...same KH!!!!

I tested pH of tap water and tank with 2 kits tap tested 7.2, tank tested 6.2????? Can't be the kit.

I tested the KH test by adding baking soda to the sample...it tracked correctly, so it is not the test...

Heres the issue, how can my fish survive (13 of them) with a CO2 level of 66-95ppm (per the table)?

Is it possible that there is such a concentration of O2 in the water (from photosynthesis) that the CO2 levels are not affecting the fish???

Thanks,
Steve
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Old 06-27-2003, 02:29 PM   #3
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I would definitely slow down the co2 output to get no more than 30ppm. During the day the fish are safe because of phto synthesis producing oxygen. but at night time the fish have to be getting stressed out. Are you using any type of water buffer to lower your ph or some sort of phosphate based additive such as novaqua?
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Old 06-27-2003, 02:34 PM   #4
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Does anyone know if running such a high concentration of CO2 prevents fish from exchanging co2 from their gills? What's the LD50 for CO2 overdose?
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Old 06-27-2003, 02:50 PM   #5
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No buffers added, just ferts...
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Old 06-27-2003, 03:57 PM   #6
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http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

Take a look at this article page from your KH you are way overdosing with Co2 id drop the C02 back if you leave it on all day try turning it off at night

the ideal Ph should be around the 6.8-7.0 ph mark

HTH
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Old 08-08-2003, 01:23 AM   #7
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I dont believe additional O2 would offset the presense of the CO2...the amount of CO2 absorbed by the fish due to osmosis would not decrease. But note the "I dont believe" part...just a theory.

As far as the CO2 level preventing the fish from getting rid of CO2 in its blood, yes it does. Osmosis works the same way either direction, so the fish would not be able to get rid of its CO2 below the level found in the water.

So I guess it is a question of 'how does CO2 harm critters?' Is it toxic like CO or what?
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Old 08-08-2003, 01:53 AM   #8
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Quote:
So I guess it is a question of 'how does CO2 harm critters?' Is it toxic like CO or what?
High levels of carbon dioxide would cause the fish to suffocate, no oxygen is available.
To completely oversimplify, carbon monoxide poisoning is kind of similar, but on a cellular level.

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Old 08-08-2003, 02:02 AM   #9
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Quote:
Originally Posted by abica
I dont believe additional O2 would offset the presense of the CO2...the amount of CO2 absorbed by the fish due to osmosis would not decrease. But note the "I dont believe" part...just a theory.
I also don't believe that O2 and CO2 concentrations are related, but are rather independant of each other, and that even though O2 will most likely be at sufficient levels during a CO2 overdose, the CO2 acts as more of a poison than an O2 replacer (Pretty sure of this, but not certain).

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Old 08-08-2003, 03:33 AM   #10
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Someone correct me (I know you will!), but doesn't the osmotic process pertain to solvents (liquids), not gasses?

Fish don't absorb CO2 through osmosis, in fact they expire CO2. No absorption of CO2 on the fishes part.

Maybe its me, but I need abica to clarify.

Mike
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Old 08-12-2003, 09:30 AM   #11
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Steve, I had the same problem with my tank last week. My pH went from ~7.0 to ~6.2 with a kh of 3 yet the fishes weren't acting stressed. I stopped my c02 production as it was pretty much constantly bubbling. My tap water quality is about the same as yours.

I'm not sure of this, but what I think may have caused it was the Nuetral Regulator I had been using when making water changes. When I read that it contains phosphates and that adding it could throw off a pH test, I switched to a different water conditioner. After slowing down the bubble rate of the c02, my water quality was ph ~7.0 kh 2 gh 15. So now I need to step up the c02 a little more. I don't know what caused my kh to drop a point. (What causes kh to fluctuate?)

Anyway, good luck... I'd like to know how it turns out for you so I can learn a bit myself.
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Old 08-12-2003, 12:53 PM   #12
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Everything I have seen out there points to the fact that my CO2 actually was that high, but because the plants were producing excessive O2 during the day, it didn't affect the fish...

We still don't know everything we think we do about this stuff (at least it isn't mainstreamed). My tank is heavily stocked, maybe that has something to do with it...

Thanks,
Steve
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Old 08-12-2003, 01:09 PM   #13
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Quote:
Originally Posted by Momotaro
Someone correct me (I know you will!), but doesn't the osmotic process pertain to solvents (liquids), not gasses?

Fish don't absorb CO2 through osmosis, in fact they expire CO2. No absorption of CO2 on the fishes part.

Mike
I think that when the CO2 content of the water is high, the fish cannot expire the CO2 they need to, since the water is more saturated than the fish, it will not move to the water.
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Old 08-12-2003, 03:05 PM   #14
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It seems like the core question is, does CO2 in solution in water displace O2 in the water?

Either way, CO2 concentrations in the water in excess of the CO2 concentrations in the the fishs blood will prevent the fish from expiring the CO2 from their gills. Gills are a passive membrane through which osmosis occurs (In both directions, O2 uptake and CO2 exhaust).

CO2 will not displace O2 in the blood because the O2 is bound to hemoglobin and CO2 will not bind to hemoglobin. Having too little oxygen is a condition known as hypoxia and too much CO2 in the the blood is hypercarbic. Hypercarbic blood causes respatory acidosis (the blood gets acidic, pH drops). The pH of the blood determines how much oxygen the hemoglobin can transport. Hemoglobin can act as a pH buffer, but this decreases the amount of oxygen it can transport and vice versa.
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