# Acceptable PH levels with CO2



## Texan78 (Nov 17, 2013)

Hello, 

Forgive me if this is in the wrong part. I have recently stepped up my aquarium hobby to doing planted tanks which is something I have always wanted to do. I have been doing aquariums for 25+ years. I recently have had the money to do a tank right and build one out properly. 

With that said, I am running C02 on my tank for the plants. It has always been a rule to me to allow your fish to adjust to the PH of your water and not try to get it perfect. The PH on my tank sits at 6.61 without C02 and drops to 6.49 with it on. I am getting these numbers from my Apex controller. I have it set up to turn the C02 on about 30 mins before the lights come on and have it go off when the lights go over for the night since it's not needed at night. With the exception of change in PH.

So my question is, what would be an acceptable drop in PH that won't stress out the fish? I have the Apex shutting off the C02 when it drops the PH to a certain number, just not sure what would be an acceptable drop to set it to. 

-Thanks


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## Darkblade48 (Jan 4, 2008)

pH drops that are associated with injection of CO2 usually will not harm livestock.

The pH drop that you currently have is perfectly safe; many users experience a pH drop of 1 whole unit with no harmful effects.


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## Coralbandit (Feb 25, 2013)

A drop checker will help you get the co2 to a "proper" level.


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## Zorfox (Jun 24, 2012)

I agree with Darkblade. Most hobbyist end up having a 1 point PH drop. However, you may want to refer to a PH/KH/CO2 chart. These three components have a direct relationship. These charts assume carbonates as being the only buffer, they usually aren't. However, it is a close approximation.


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## Texan78 (Nov 17, 2013)

I woke up this morning and the PH has come up to 6.79 since the CO2 has been off over night. So it looks like it's coming up to a that "perfect" target so to say which in reality really isn't perfect since some fish like lower but it's a good starting point. I think I will keep it off for a couple days so I can see where it settles at and go from there. I do have a drop checker but I am not sure how that correlates with this as that just shows the amount of CO2 being injected. 

Let's say it does come up to 7+. So a swing of 1 point would be ok? I was always told constant swings of more than .03 is bad for the fish. Is this not true? So would it be ok to set it to not go lower than 6.00? 

-Thanks


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## Zorfox (Jun 24, 2012)

Forget PH ranges, KH, charts, chemistry and everything else for a while. The truth is, you want to *SLOWLY* increase your CO2 one step at a time until you notice distress in your inhabitants. *Then* return to the setting you had just prior to that. This would be the highest possible level your setup can handle. Never increase CO2 unless you will be there to monitor your inhabitants reactions.


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## tetra73 (Aug 2, 2011)

Just want to add to the PH co2 chart. Your CO2 is safe because your CO2 level is hardly enough for optimal plant growth. What is your KH level? Ideally, you should strive for 30ppm of CO2 level. Your plants can grow faster assuming you have all the necessary ferts. People turn up their CO2 really high, into the near 50ppm because they have a lot lighting. They want the plants to grow faster and healthier AND without having algae problems. My CO2 level is close to 50ppm. I have my CO2 to turn on 2 hours before the light comes on. It takes time for the CO2 level to reach to certain range. And I don't want my light to turn on until my CO2 level is above 30ppm. I don't know about your light intensity and your fert dosing methods. Is hard to say if you should or shouldn't try to increase your CO2 level.


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## tetra73 (Aug 2, 2011)

Zorfox said:


> Forget PH ranges, KH, charts, chemistry and everything else for a while. The truth is, you want to *SLOWLY* increase your CO2 one step at a time until you notice distress in your inhabitants. *Then* return to the setting you had just prior to that. This would be the highest possible level your setup can handle. Never increase CO2 unless you will be there to monitor your inhabitants reactions.


Is a bit more complicated than that. Yes, you should increase slowly until you see stress on the fish. This could mean a lot of things. Maybe you don't have enough gas exchange. You can stress out your fish at less than 30ppm if you don't have enough gas exchange. You should strive for max gas exchange in order to reach your desired CO2 level, without causing harms to your fish.


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## Zorfox (Jun 24, 2012)

tetra73 said:


> Is a bit more complicated than that.


Naturally, things like using a wet/dry filter, increasing surface agitation or removing covers to improve O2 levels for example will allow one to have higher CO2 levels. However, without changing things to improve O2 exchange, not to mention CO2 uptake and degassing, this will always be the maximum setting for CO2 in an existing particular setup. CO2 delivery should never be a one step "set it and forget it" thing.


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## Jeff5614 (Dec 29, 2005)

As you can see there are as many opinions on CO2 as there are body parts so I'll share the best way , just kidding. A one point drop as mentioned above is a pretty good number to shoot for. You want to get the degassed pH reading from your tap if that's what you use to fill your tank. Reason being that you may not be degassing all of the CO2 from your tank. Take a sample of your water from the tap, allow it to sit for 24-48 hours and then measure the pH. That will be your baseline. From there you'll want to aim for a one point drop in pH. You'll want to get there slowly by gradually increasing your CO2 over a few days. Don't rush it and allow the fish time to adjust and watch them for signs of stress. Ideally you should hit that 1 point drop within an hour or so of lights on and maintain it steadily throughout the photoperiod. You can do this quite easily with a combination of good circulation and surface agitation. Since you have a pH meter it should be easy enough for you to do.


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## Coralbandit (Feb 25, 2013)

Darkblade48 said:


> pH drops that are associated with injection of CO2 usually will not harm livestock.
> 
> The pH drop that you currently have is perfectly safe; many users experience a pH drop of 1 whole unit with no harmful effects.


I agree with this from my experience.
My tank(180G) goes from 7.4 to 6.4 daily.I use a milwaukee contorller and pressurised co2 with a sera reactor.The importance of the drop checker should not be overlooked.You want it to turn green.It is important that the fluid in it is 4 dkh and not tap/ro/or tank water.
I get mixed signals from you as you added co2 for plants ,but are concerned about fish?I too share your concern,but have found no issue in my pH "swing".If your drop checker isn't green then the co2 is not enough to make much of a noticeable difference with your plants.
My fish are way more important then my plants(sorry everyone!) but without proper application of the co2 it is just wasted.
My tank has discus,cardinals and rummynose so if the swing was going to "mess" with anyone I expect I would have seen it by now.


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## tetra73 (Aug 2, 2011)

Coralbandit said:


> I agree with this from my experience.
> My tank(180G) goes from 7.4 to 6.4 daily.I use a milwaukee contorller and pressurised co2 with a sera reactor.The importance of the drop checker should not be overlooked.You want it to turn green.It is important that the fluid in it is 4 dkh and not tap/ro/or tank water.
> I get mixed signals from you as you added co2 for plants ,but are concerned about fish?I too share your concern,but have found no issue in my pH "swing".If your drop checker isn't green then the co2 is not enough to make much of a noticeable difference with your plants.
> My fish are way more important then my plants(sorry everyone!) but without proper application of the co2 it is just wasted.
> My tank has discus,cardinals and rummynose so if the swing was going to "mess" with anyone I expect I would have seen it by now.


Put away the drop checker. Seriously, I have "used" it or just left it in the tank for 2 years. I had nothing but problems with BBA and certain plants just didn't do that well. When I switched to the CO2/PH chart 4 months ago and understood that the presence of CO2 in the water would cause the PH to drop regardless of your KH or your water quality, I haven't used my drop checker for over 4 months....ever since I have converted my tanks to all dirt. No BBA outbreaks. Unhealthy plants tend to get some tinny BBA but the plants were soon trimmed. My DHG carpet is doing pretty well after 3 months of planting it. And I am using 2 T5HO bulbs (total of 78w) + 2 T8 light strips on my 40g. Is high light for sure. I only get GSA on the glass.


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## Zorfox (Jun 24, 2012)

Jeff5614 said:


> As you can see there are as many opinions on CO2 as there are body parts


Actually, I think we all agree here, oddly enough lol. I agree with everything said so far with one exception. I'm with tetra73 on the drop checkers. They're nowhere near responsive nor accurate enough to use as a real measure. PH/KH relationship is superior and just as easy (easier with a PH controller) as an indicator. Of course, the "king" of all indicators should remain your inhabitants (including plants) IMO.


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## Texan78 (Nov 17, 2013)

Thanks for all the feedback, it is very much appreciated. Here is a little background on the tank. I just broke this tank down a couple weeks ago and redid it to make it a planted tank so it's pretty much a new set up. It's 55G 48X12X12, new 90G long is going to replace this probably in a month. I haven't decided yet, I really started thinking about it when I started hardscaping and planting this tank that I would be happy with something bigger. Anyways, here is what is on it. 

Fluval 406 Canister filter
2 Hydor Koralia 600 GPH Pumps on each end for surface agitation and circulation. 
Apex controller with lab grade PH and ORP probes. 
Corallife Turbo Twist UV Sterilizer (Only installed it in case I need it one day)
5lb C02 with Aquatek regulator with integrated solenoid connected to the Apex 
Bubble counter, and defuser from GLA. Currently it is at 2 bps
Lighting is a Marineland Reef Ready LED 10K 48" light. This is being replaced with a Finnex Planted + which has been ordered. Only using the reef ready light since I needed a light and replaced the ones on my reef tank with SOLS. Thinking about using two of the Finnex Planted +, would that be overkill on light?
300W Aqueon heater, nothing special controlled from the Apex. 
Tank does have a lid but will probably take them off once the driftwood sinks. 

When I set up this tank or any tank I always take a sample of the tap water and let it sit for a couple days and take my baseline measurements from that and start from there. When I turned the C02 on today the PH was 6.81 @ 11AM now at 2:30 PM CST it is sitting at 6.39. Without getting techincal I was just curious of what a extreme low PH would be so I could set the Apex to shut it off if the PH drops to low. It seems 1. is the general rule from what I am reading. It has only dropped .46 in 3 1/2 hours so that seems to be fairly gradual. Mainly I am just looking for a bottom line PH to not go lower than.

-Thanks


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## samee (Oct 14, 2011)

After the 24 hour test my water was 8ish. But I didnt go by that. In the morning my tank water is around 7.2. Ive set it to 6.1. I dropped it to 5.9 at one point and my fish were floating at the surface gasping for air. So I set it back to 6.1. It takes about 15 minutes to drop from 7.2 to 6.1.


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## Zorfox (Jun 24, 2012)

I think the best advise I can give you Texan is this. Adjust your CO2 level slowly upwards in small steps. After no ill effects are noticed for 24 hours move to the next step. Continue this until the next step results in distress of inhabitants; if distressed, return to the previous increment.. *NOW* look at you saturated PH. Go no lower than that unless changes are made. That's your maximum safe level for the current conditions.

How close to death do you want to play? How confident are you? That's when knowledge and experience comes to play. Conditions change easily affecting CO2 levels. This is where the experience does play a role. Yet, the novice and experienced alike will never know the PH limit if we never observe it. Watch your fish not your meter.


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## plantbrain (Dec 15, 2003)

Zorfox said:


> Actually, I think we all agree here, oddly enough lol. I agree with everything said so far with one exception. I'm with tetra73 on the drop checkers. They're nowhere near responsive nor accurate enough to use as a real measure. PH/KH relationship is superior and just as easy (easier with a PH controller) as an indicator. Of course, the "king" of all indicators should remain your inhabitants (including plants) IMO.


I concur.

I typically test things this way:
Have a nice tank growing plants very very well. Next have more than 1-2 such tanks. 

Now you have a reference and some stat's(more than 1-2 tanks) to support it. Now you measure each tank. You can use the pH meter to measure RELATIVE CO2 via pH drop. 

KH: Lamotte test kits get pretty close, +/- 4ppm of Alkalinity. 

There might be some sources of non Carbonate KH, typically polyphosphates to help keep the KH up in some tap waters. This ONLY makes folks believe they have more CO2 than they really do, never less. So the error is always slanted to the fish using this method, as it should be.

CO2 water standard references?
Dry ice, added to a large volume of DI water(say 4 to 20 liters) and some baking soda to make a known reference KH and a known CO2 ppm or mg/l solution. Measure the pH and see.

If you match the KH in the standard to that of your aquarium, but only use baking soda to do it, now any difference will be due to non carbonate alkalinity. If they match, then you know you are in good shape.

Adding say 500 milligrams of dry ice to say 10 liters= 50 ppm of CO2 or 50mg/l.

Dry is available and you can buy it at many grocery stores these days and party places. Main thing is to have a pH meter and a sealed container where you can insert the pH probe into the water. Pop the lid/cork top etc, and toss the dry ice in fast and sealed the lid back. Wait till it's dissolved for about 30 minutes. Swish the water around good to mix. 

One of the few relatively cheap methods to make a known CO2 ppm solution that will not degas on you right away.

I use about 1.2 pH drop or a tad more in some cases. 
Mostly look at the plants though.


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## Texan78 (Nov 17, 2013)

samee said:


> It takes about 15 minutes to drop from 7.2 to 6.1.


Whoa! That's pretty fast. Mine isn't coming close to dropping that fast at all. Is that normal? If mine isn't dropping that fast then that should be a good sign right?

I guess a better question would be how to tell if your fish are stressed? Different fish react differently to different PH levels. I understand what people are saying and it makes sense to let the fish be the judge of it. Lets take the C02 out of the equation all together. Under normal circumstances, what would be considered a unsafe and dangerous low PH for fish?


-Thanks


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## tetra73 (Aug 2, 2011)

Texan78 said:


> Whoa! That's pretty fast. Mine isn't coming close to dropping that fast at all. Is that normal? If mine isn't dropping that fast then that should be a good sign right?
> 
> I guess a better question would be how to tell if your fish are stressed? Different fish react differently to different PH levels. I understand what people are saying and it makes sense to let the fish be the judge of it. Lets take the C02 out of the equation all together. Under normal circumstances, what would be considered a unsafe and dangerous low PH for fish?
> 
> ...


Well, I generally measure the ph in the middle of the night when most of the CO2 is supposed to be degassed. I have an air pumping running at night. I just use that ph value as my reference, which is around 7.1, with a 3dKH. By the end of the light cycle, my ph value is about 6.3 to 6.2. Pretty close to 50 ppm. However, it takes 2 hours for my CO2 to reach to ph of 6.4 to 6.3. Around 30+ppm of CO2. 

Here is the thing. You can speed up your CO2 level saturation by adding more CO2 very quickly. So, you would reach to your desired CO2 level pretty quick. The drawback is that, most likely, the CO2 level would get built up too fast and too quick. You may have too much CO2 by the middle of your light cycle. You don't want that because you would gas the fish at end of the day. If you have a reliable ph controller, you can program it to turn off the CO2 at your desired ph value. Like me, I don't use a ph controller. So, I have to add my CO2 very slowly and to rely on a longer CO2 cycle time in order to reach my desired CO2 level. That's why it takes me 2 hours to reach more than 30ppm of CO2 level. By the end of the CO2 and light cycles, my CO2 level should be around close to 50ppm. 

You can try to see if you can reach your desired CO2 level per the chart reference in 1 hour. Adjust your CO2 input as much as needed. Measure your ph by the middle of the day to see what is your CO2 level is at. Then, another reading by the end of the day. It took me a month to finally dial down my CO2 level since I was experimenting with using different CO2 reactors and filters.


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