Not enough Co2 without being too acidic! - The Planted Tank Forum
 
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post #1 of 14 (permalink) Old 08-07-2011, 01:38 PM Thread Starter
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Question Not enough Co2 without being too acidic!

This is, I'll bet, a pretty dumb question for those knowledgeable. I've been keeping aquatic plants for years, but have recently taken things full-bore and built a new stand with canopy that has big light output going in cycles (I have morning/ noon/ evening and lunar cycles), and I purchased a C02 injection kit.

The tank is just cycling in right now (75 gallon) and I have some bulbs planted and some mature onion plants (I used a Flourite base, split the tank 1/2 sand 1/2 gravel).

My issue is that with the Co2 injection, I have a PH of 7.2 (I keep catfish and don't want to go acidic) and a Kh of 3. So from what I'm seeing that means my tanks capacity for Co2 is something like 9ppm, and I need this to be more like 23ppm.

What do you do with this? I can't raise the hardness (and that sounds bad for the fish) and the PH is already kinda high for tropicals it seems (don't they prefer more alkalinity?).

I'm totally new to the boards, I've looked allot online, but its difficult to find info that answers this question. What can I do to achieve a Co2 level optimum for plants AND maintain a hardness/ acidity that's optimal for fish??

Thanks in advance!
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post #2 of 14 (permalink) Old 08-07-2011, 01:53 PM
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inject c02 sure it will lower the ph. you dont wanna go below 6.5 6.4 because bacteria becomes like 80% less effective.. so i'd suggest a naturally way to raise ph being quartz or other hard stones.( im not sure of the list)
you'll want to aim for about a 1 ph drop after c02 turns on. supposedly that equals 30 ppm. TOO much light also and you will have a problem with algae.. less light means less need for c02

without a good balance of light c02, and fertilizers and you will have algae and poor plant health.. start reading articles on here they will explain most of your questions, and even some you don't yet have

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post #3 of 14 (permalink) Old 08-07-2011, 03:22 PM Thread Starter
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Thanks for responding.

Does raising the Ph, in turn, limit the amount of Co2 that can be in the water? I started out with over 8, injecting Co2 brought me down to around 7.1-7.2. Kh is about at 3. Adding Co2 raises my Kh and that seems to (from what Ive read) limit how much is absorbed.
Do I totally misunderstand the relationships here?

Damned science *shakes fist*.
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post #4 of 14 (permalink) Old 08-07-2011, 04:21 PM
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pH is influenced by a number of factors in an aquarium.

Of those factors, the most important to fish is hardness; which is the amount of dissolved minerals like calcium and magnesium. Normally, hardness is the only major factor affecting pH. So it's possible to give a simple pH recommendation for certain species, rather than a hardness recommendation which fewer people would be comfortable or familiar with.

But since adding another major pH affecting factor like CO2 invalidates the simple pH/hardness relationship, it also invalidates those simple pH recommendations.

You will find that adding CO2 also affects your hardness tests. That's because simple hobbyist-grade tests do not measure hardness directly. Like the pH recommendations for fish, they too assume that hardness is the only major factor affecting pH. When that is true, they can infer the hardness by measuring how difficult it is to shift the pH. Again, adding CO2 invalidates that simple pH/hardness relationship, so CO2 reduces your measured hardness.

However, the water's mineral content remains the same; so your true hardness is unaffected. Consequently, the health of your fish is unaffected too.

Adding CO2 does not increase hardness, either measured or real, as you stated. If you're seeing this, then there is either something seriously wrong with your test affecting your measured hardness, or there is some calcium-based substance in your aquarium that's being dissolved by the CO2 affecting your real (and measured) hardness.

Damned science. Hope I've made it clear.
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post #5 of 14 (permalink) Old 08-07-2011, 04:25 PM
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Your pH will be normal in the morning and drop during the day as gas is added, all the fish I have ever had are fine with the pH drop and only bothered by being gassed to death. My kH is much lower than yours and I have never had any problem with the so called limited buffering capacity that I know of, if I were you or me just try to get a good amount of C02 in the tank by watching the plant health and growth along with the reation of the fish. You can test pH and kH and have a drop checker and never really know the amount of gas in the water but these methods can be guides to making adjustment in gas amounts but are rarely spot on acurate. You don't want to add so much C02 that your pH drops so low that your nitrifying bacteria slows to a point little activity and by adding oxygen to the water column with air stones/wands during the lights/C02 off period you can help build a larger base of nitrifying bateria which will help the tank as a whole perform better, so example lights/C02 on 8 hours, air on 16 hours, can equal good things, good luck.

Don't forget about circulation to distribute C02, nutients, etc. equally around the tank.


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post #6 of 14 (permalink) Old 08-07-2011, 05:03 PM
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5.8pH and a tested 2dKH on my injected tanks with drop checkers a pale yellow/green being correctly set with 4dKH solution.

I too had a hard time with this and the membership helped out a bunch.
don't know if any of this will help you out or not.
https://www.plantedtank.net/forums/fe...h-hazards.html

page from the krib too
http://aquaticconcepts.thekrib.com/A..._Chemistry.htm


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post #7 of 14 (permalink) Old 08-07-2011, 06:15 PM
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You might consider that less light requires less CO2 or just using more light for a few hours later in the day after CO2 levels have risen.
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post #8 of 14 (permalink) Old 08-07-2011, 07:22 PM
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Well if your tap water ph was 8....if you can inject enough co2 to bring it to 7, then you're golden.
That should be plenty of co2, and I don't know of many fish that can't do just fine in 7 pH.
Increasing your kH doesn't limit how much co2 you can absorb, as far as I know, someone will correct me if I'm wrong, though.
an increased kH tends to reduce how much your ph fluctuates with co2, so if you were using one of those charts to determine ppm of co2, then you might assume you had less co2, but you still have the same amount being pumped in.

Look into getting a drop checker.
And if your pH is too low, things like limestone, crushed coral, or crushed marine shells will race your pH.
There are also many products available for african cichlids that can do the same thing, and some people believe they are more stable than things like crushed coral.
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post #9 of 14 (permalink) Old 08-07-2011, 07:25 PM
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DarkCobra is correct. You will still have the same number of dissolved solids in your tank. Your fish will be fine.

Just keeping on keeping on....


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post #10 of 14 (permalink) Old 08-07-2011, 07:29 PM
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Simple baking soda will raise carbonate hardness but beyond 2-3dKH there's no reason to do it. Low readings on pH driven by CO2 injection don't affect many if any fish at all.
The TDS or mineral content of what they are swimming in is what effects fish one way or another. Either hard water or soft and the range is broad before issues occur.


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post #11 of 14 (permalink) Old 08-07-2011, 08:33 PM
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First things first, if you bought the kit that uses little tiny CO2 cartridges for CO2 injection, return it. It's relatively economical to start up, but you could buy a new car with the amount you'd spend on refills for a tank that large. :-) Just in case.

This paper is a good introduction to the interplay between pH, dissolved carbon dioxide, hardness, and KH (aka alkalinity.) It's intended for aquaculturists, but the chemistry is the same for an aquarium.

It looks like you have a pretty good understand of the interplay between CO2, pH, and KH, however, the value you've come up with isn't the maximum capacity of the water, it's the equilibrium value for the concentration of CO2 given our atmospheric conditions. You can force far more CO2 into solution and it will tend to outgas to the atmosphere.

There is a lot of sloppiness in the terms people use, hardness, carbonate hardness, GH, KH, etc. I've been reading a lot to try to pick out the meanings of these things and honestly, you see a lot of cockeyed advice on this forum and others. They can be strange ideas to begin with, and their interactions are complicated.

Hardness (AKA GH: concentration of ions with charges greater than +1, typically calcium and magnesium but iron is another common one) has little to nothing to do with your pH in and of itself. It's a measurement designed to let people know how much soap to use that has been adopted as a convenient value for a host of other things, whether it is appropriate or not. It's important that water not be extremely soft because fish and shrimp require some level of dissolved calcium and magnesium for metabolic processes. The multivalent ions are technically weakly acidic, and they also help to provide buffering against additional bases added to solution. These aren't very important to us usually because of the vastly stronger carbonate buffering that is also occurring, and for practical purposes can be ignored.

KH (AKA carbonate hardness: concentration of carbonate and bicarbonate in water, closely related and often synonymous with alkalinity, but alkalinity also includes concentration of hydroxides and borates) is a measurement of the buffering capacity of your water. As KH rises, pH also rises, but fluctuations in pH decrease. Water with a high KH has very very stable pH values, but that pH is typically somewhat high. Higher KH means that additional CO2 is dissolved in water at a given pH when it is at equilibrium with the atmosphere (i.e. less outgassing occurs at a given pH.) That's rarely a consideration for us.

pH (the opposite of the base 10 logarithm of the concentration of hydrogen ions in solution) is important to some species of fish and inverts, but for the vast majority of species, the stability of the pH over time is more important (as long as the pH is within reasonable bounds, of course.) As long as you have a reasonable alkalinity (buffering capacity) you should be fine.

The reason that so many of these things get confused and conflated is that one typical source of all of them is calcium carbonate (limestone) with calcium magnesium carbonate (dolomite) being another. When water comes from a limestone or dolomite aquifer, it tends to have high GH, high KH, and high pH. The three values are not necessarily linked though, at least to the extent that many people believe. The water from my well, for instance, has a pH of 8, a GH of 2.5, and a KH of 14. It's also entirely possible to have a very low KH and a very high GH.

In short, and to actually answer the question you originally asked, your water parameters look fine to me and you shouldn't have to worry about CO2 injection. The 9ppm value you found is related to the equilibrium concentration that your water would have with the atmosphere, not the amount that can be dissolved in your tank. If you find that your pH is moving around significantly from day to night you can try to increase your KH but you probably won't need to.
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post #12 of 14 (permalink) Old 08-10-2011, 12:44 AM Thread Starter
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Thumbs up

Thank you guys SO much.

This is seriously one of the best boards ever for information.

I've cranked the Co2 a bit more and am hovering around 6.9 for Ph.

I was using the chart showing the Ph/Kh relationship to determine Co2 levels. So maybe thats just a B.S way of doing it.

My lights aren't up yet, but I do have plenty and will be running it on cycles like someone mentioned. Also, I have two airstones that come on at night. My Co2 setup ideally should just shut off then because it fires up still but the gas I assume is just vented with the agitation on the surface (?)

I have an inline diffuser and a bubble counter. Though the bubble counter seems to be useless to me, because the bubbles stop right away, then I turn up more pressure until I have 1/sec but it stops again... I do this over and over until I have pressure putting out to the line and the bubble counter runs about 1/sec (I just assume thats right). But after the solenoid shuts off and the line bleeds into the diffuser.... and it comes on again after a while, the bubbler is crazy until pressure is built up again and gas is pushing through the diffuser.

I have ordered a different inline diffuser. Been using this:
[Ebay Link Removed]

Maybe these are junk? It was old, so I'll try a new one and see.

Thanks again. I ordered driftwood, so that'll totally throw my params off anyway at this point, but it sounds like my Co2 level is fine, and I should think of it more as the difference I've seen in Ph prior to injection, rather than rely on the charts assumptions about what my initial water was like.

+1000 internets to you all!
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post #13 of 14 (permalink) Old 08-10-2011, 12:46 AM Thread Starter
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Ps. Ebay link was removed. If you're curious.. do a search for "Aquarium tank CO2 Atomizer system" that diffuser is what I have.
Seemed like a good idea at the time. Maybe it is really good...
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post #14 of 14 (permalink) Old 08-10-2011, 01:21 AM
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too give you an idea. my drop checker is yellow, my ph goes from 7.6 to 6.4 when lights and c02 are on.. im assuming its 7.6 because my ph test kit can't go any higher... so um im hovering between 60-80 ppm of c02. i haven't tested with my c02 kit lately but i just increased it after my shrimp acclimated.
so to those of you who think 30 is the limit i have pictures of my Drop checker. and i can take one of ph tomorrow..

also if you are producing a fine mist of bubbles and the majority aren't reaching the surface, ur diffuser is fine.
and correct the difference in ph is what you are looking for. the chart is merely a guideline. it isn't accurate for anything but a perfect tank.

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