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Discussion Starter · #1 ·
According to my ph @ 6.6 and my kh @ 12 I'm running @ 90ppms. Is this right and if so shouldn't my fish be gasping for air?
 

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I've heard (YMMV) that CO2/O2 are not mutually exclusive. You can have 40% CO2 saturation and still have 100% O2 saturation.

The point where fish begin to gasp at the surface is when either a) the O2 content is low, or b) when the CO2 reaches toxic levels. This means that even though you may have 90 ppm CO2, your ambient oxygen levels probably haven't changed.
 

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Discussion Starter · #3 ·
Thanks Error, that makes sense....Another question; The tank we are speaking about is 100% RO water. I just tested the water from the tap. Both kh and gh are 1...my question is why is my kh 12 and my gh 20 in my tank? Could it be my Onyx sand substrate?
 

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Edward has done a lot of research into the effects of substrate on water hardness. You might want to ask him.
 

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On second thought, you can probably test it yourself.

Stick some plain tapwater in a container with some of your substrate, and some in a container without it. Test them a week or two or three later.
 

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I have Onyx and eco in my substrate. They will both buffer the kh and gh. My gh raises about 1 degree every 2 days and my kh about 1 degree every 3 days. Both have excessive Ca and Mg. I am not too scientific but I know they both raise it.
 

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Discussion Starter · #7 ·
Guy's thank you...I think that's the problem. Now i'm wondering if I should change my substrate as well.
 

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Yeah I get the same from one of my tanks with eco-complete. The more acidic the water the quicker it will dissolve these elements out of the substrate. I wouldn't change it personally, it's not something I consider problematic, just start mixing RO and tap or reconstitute the RO water so that you are maintaining a stable hardness and PH rather than letting it fluctuate a lot between changes. Your plants won't care either way, your fish will thank you for it :)

Giancarlo Podio
 

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It shouldn't matter what your KH or GH is as far as substrate influences are concerned. The CO2/pH relationship is still valid. However, it is NOT valid when you have other sources of acids and bases that are not carbonic acid or carbonate. IIRC, decaying matter in the substrate will release acids. Peat and wood do the same. These will throw off the pH scale. Since the scale is log based, as outside acid sources are added, you get an artifical exponential "CO2 raise"

As for fish gasping. I recall reading somewhere that it wasn't O2, but actually CO2. If the levels are too high int he water, then the the fish cannot exchange it out of their bodies nearly as efficiently. ...may or may not be true. Just what I recall.
 

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Gomer said:
As for fish gasping. I recall reading somewhere that it wasn't O2, but actually CO2. If the levels are too high int he water, then the the fish cannot exchange it out of their bodies nearly as efficiently. ...may or may not be true. Just what I recall.
You recall correctly. I asked that exact question on another board a few months back.
O2 saturation in the fish blood has to be lower than ambient (water) across the gills and CO2 has to be higher for transfer to take place. So if CO2 level in the water are at the same level or higher than in the fish's blood no or minimal exchange take place.
Fish are gasping not because of lack of O2 in the water but because of buildup of CO2 in their blood
 
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