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post #1 of 21 (permalink) Old 02-16-2010, 08:57 AM Thread Starter
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Lowest safe pH?

For the past two weeks, I've been running my aquarium at 6.2 pH.

I'm doing this because I read that low pH makes CO2 more available to plants, and that inspired an experiment. My pH was relatively high due to my tapwater's high KH (6.6 pH, 8°KH). CO2 couldn't be increased further without fish gasping, and I don't have RO/DI water; so I lowered the pH with dilute hydrochloric acid. The result is a significant improvement in plant growth and pearling.

But I just read that biofilters may shut down under 6.5 pH.

I don't appear to have caused immediate harm, as ammonia and nitrate are undetectable. However, I wonder about long-term effects on biofilter/fish/plants, and would like a second opinion.

Does anyone have scientific data on lowest safe pH, or experience running an aquarium long-term at low pH?
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post #2 of 21 (permalink) Old 02-16-2010, 10:19 PM
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I believe you have to get into the <6.0 range to get affects such as you are worried about..

I am thinking of going the hydrochloric acid route as well..what size tank,and what ratio did you use..

I have hard water myself and am considering this option..

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post #3 of 21 (permalink) Old 02-16-2010, 11:04 PM
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I assume that the HCL would be added at every water change?

Please tell us more.
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post #4 of 21 (permalink) Old 02-16-2010, 11:11 PM
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Actually I am not sure if it would work for me..I am needing to lower both KH and GH..gaaaaaa...

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post #5 of 21 (permalink) Old 02-17-2010, 02:10 AM Thread Starter
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Thanks, Zenfish.

My experiment addresses only CO2 availability to plants; it probably won't help with any other issues caused by high GH/KH.

Here's details as requested. I'm going to be verbose since hydrochloric acid requires some respect.

Hydrochloric acid (HCl) is commonly sold by the gallon as muriatic acid for lowering pH in pools, costs about $10, and is about 32% concentration. At this concentration it's highly corrosive; and it "fumes", releasing visible acidic vapor clouds into the air. Take care not to breathe the fumes or spill it. If it gets on your skin, rinse it off quickly. I work with it in a tub with an inch or two of water, so that any spills and splashes are instantly diluted; and use plastic measuring cups and funnels, never metal.

I learned the hard way that once opened, it can continue to leak fumes even if the lid is on tight. It damaged a metal utility shelf and other items near it. So the first order of business is to dilute it to the point it no longer fumes. Divide it equally between two other plastic gallon containers, then top off with water. You now have a 16% solution which can be stored and handled more safely. Remember to accurately label this, and all other solutions you create.

You may be able to skip this step - some stores sell "Safer Muriatic Acid", which is already prediluted to 15% concentration. If you can find it, use it!

I then use that some of that solution to make a more dilute final solution. Currently, I measure 1.25 cups of 16% HCl into a two liter bottle then top that off with water. At this dilution, it's no more dangerous than vinegar. In fact, I've tasted it and found it similar to white vinegar; though I won't be making any vinaigrette salad dressing with it!

1 tsp. of that solution will lower 1.5 gallons of my 8°KH tapwater to 7.2 pH. I use the two liter bottle to fill an old Amquel bottle with a flip-top, which is more convenient to use.

I arrived at these measurements experimentally, by mixing up smaller batches and testing their effect on tapwater pH *outside* the aquarium, then scaling up to two liters. You can do the same to come up with a final solution and concentration that is most useful to you.

When using this to adjust aquarium pH for the first time or in a new way, add a fraction of what you think you need, wait a bit and test pH, then add the next fraction, and so on. This will help prevent catastrophe if you've made an error in your measurements.

Large pH changes to a tank should be done slowly over hours.

To adjust an aquarium's pH, I put some tank water in a cup, add the needed amount of solution, and slowly pour it into my HOB's outflow.

To readjust aquarium pH after a water change, I do the above after refilling the aquarium, but with a lesser amount. For example, if it took 10 tsp. to adjust the aquarium to a certain pH in the first place, and I perform a 50% water change, it will take 5 tsp. to re-establish that pH. The transient fluctuation in pH during the water change has never harmed anything so far as I can tell.

Some people frown on using HCl to adjust pH. They say it can create large and uncontrollable pH swings, and pH rebounds over time. I guess that's possible if you have low KH, or measure incorrectly; or have something in your tank actively pushing pH towards a certain level, like a phosphate buffer or reactive substrate. Personally, I've never had any problems. HCl works great for me, and the $10 bottle will last me a lifetime. Your results may vary.

My tank is 46g, and I wanted to go from 6.6 to 6.2 pH. So:

(38/1.5)/(1.4/0.4)=7.24 tsp. of solution

Where:
38=the water volume in gallons to adjust (estimated water in my 46g)
1.5=the amount of tapwater in gallons for which I know the pH shift for 1 tsp. of solution
1.4=the known pH shift for 1 tsp. of solution in 1.5g of water
0.4=the desired pH shift

That formula usually gets me in the ballpark, but since I've never done an adjustment quite like this before, I took my own advice and went slow with 2 tsp. initial dose, followed by additional 1 tsp. doses until I reached target pH.

Unfortunately, I seem to have lost my notes tallying up how much I actually added. So I'm going to go slow again next time I do a water change. Since I do 33% water changes, the dose will be 1/3 of what I originally added.
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post #6 of 21 (permalink) Old 02-17-2010, 02:30 AM
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Safer:
Lower the KH to around 3 degrees, then add peat moss to the filter.

I have seen all sorts of posts about nitrifying bacteria, and they all seem to agree that somewhere around pH 6.2 they are seriously in trouble, and by 6.0 they are incapable of doing their work. (They thrive best at pH from about 7.0 to 8.0, and need some minerals to survive). This may not be as bad as it sounds, as long as the tank is full of thriving plants. However, if something happens to the plants, and ammonia shows up in the tank, then at that pH it will all be in the ammonium form (NH4+) and this is not so harmful. However, if something then happens and the pH rises, the NH4+ can change into NH3, which is toxic.

Much safer, if it will work for your fish and plants, is to aim for a pH not too far off neutral, then allow CO2 to drop it into the mid 6s or a bit lower.
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post #7 of 21 (permalink) Old 02-17-2010, 02:34 AM
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I see what you mean cobra.You are lowering KH so you dont have to inject so much co2.If I recall KH mops up co2 so the more you have,the more co2 one has to inject..?

I think I read somewhere that hydrochloric acid basically,somehow,destroys KH..Correct me if I am wrong,and does not do the same for GH...

I also think cobras post should go somehwre for a sticky on people wanting to try this method for adjusting PH for co2 availability,if it hasnt been done already..
Zen

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post #8 of 21 (permalink) Old 02-17-2010, 03:25 AM
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Originally Posted by zenfish View Post
I see what you mean cobra.You are lowering KH so you dont have to inject so much co2.If I recall KH mops up co2 so the more you have,the more co2 one has to inject..?

I think I read somewhere that hydrochloric acid basically,somehow,destroys KH..Correct me if I am wrong,and does not do the same for GH...

I also think cobras post should go somehwre for a sticky on people wanting to try this method for adjusting PH for co2 availability,if it hasnt been done already..
Zen
KH does not "mop up" CO2, and having a high KH does not cause you to have to add more CO2 to the water. All that having a high KH does is change the mix of carbonates, carbonic acid, and dissolved CO2 in the water for a given total amount of CO2 in the water. The CO2 is just as available at a KH of 6 degrees as at 2 degrees. Furthermore, lowering the pH with acids is a big exercise for very little benefit. Unless you are trying to breed some fish that simply won't breed at a pH above some value, there is no reason to tinker with the pH at all. And, don't forget, CO2 is very, very cheap, so the easiest, safest, best and only way to get more CO2 in the water is to add more.

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post #9 of 21 (permalink) Old 02-17-2010, 03:56 AM Thread Starter
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Quote:
Originally Posted by Diana View Post
Safer:
Lower the KH to around 3 degrees, then add peat moss to the filter.
I appreciate the tip, but money and space are limited; so a RO unit is out of the question for now. And I don't want to use peat moss. I've been using HCl as needed for years, and I'm fairly confident in my ability to use it safely.

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Originally Posted by Diana View Post
I have seen all sorts of posts about nitrifying bacteria, and they all seem to agree that somewhere around pH 6.2 they are seriously in trouble, and by 6.0 they are incapable of doing their work.
Aha! Your wording helped me find what I couldn't find before. I should have been searching for "nitrifying bacteria ph", not "biofilter ph". I just found this:

http://www.bioconlabs.com/nitribactfacts.html

According to this, Nitrosomonas growth slows below 7.0, stops at 6.5, and all nitrification stops entirely at 6.0.

If this is true, then every tank which runs at 6.5 or below will eventually lose its biofilter, as the Nitrosomonas will die from old age and not be replaced. That's probably quite a few tanks around here...

I wonder if this info was based on short term tests, and if low pH over an extended period might selectively breed a strain of low-pH resistant Nitrosomonas.

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However, if something happens to the plants, and ammonia shows up in the tank, then at that pH it will all be in the ammonium form (NH4+) and this is not so harmful. However, if something then happens and the pH rises, the NH4+ can change into NH3, which is toxic.
I knew about that tricky little bit of chemistry. But I didn't know that plants had such an affinity for ammonia; to the point of making the biofilter redundant, maybe even counterproductive since the plants would appreciate the extra ammonia. Then again, the algae might like the ammonia too...

Hmm... This is only leading to more questions, and more ideas for experiments.
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post #10 of 21 (permalink) Old 02-17-2010, 04:39 AM Thread Starter
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Quote:
Originally Posted by zenfish View Post
I see what you mean cobra.You are lowering KH so you dont have to inject so much co2.If I recall KH mops up co2 so the more you have,the more co2 one has to inject..?
I am lowering pH to make CO2 more available to plants, while keeping the CO2 injection rate the same.

The change in pH is what's important here. HCl does have an effect on KH, but it's much easier to understand what's going on here if you look at this strictly from the pH point of view.

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Furthermore, lowering the pH with acids is a big exercise for very little benefit...And, don't forget, CO2 is very, very cheap, so the easiest, safest, best and only way to get more CO2 in the water is to add more.
I'm sorry, but I'm going to have to argue that.

When I first switched to pressurized CO2, my plants pearled. Over a couple of weeks it went away, and never returned.

You say add more CO2. Well, I turned it up until the fish gasped, but no pearling. On top of that, I experimented with extra ferts and lights, reduced surface agitation, you name it - still no pearling.

That bugged me. Maybe it's silly, but I viewed my inability to make my plants pearl again as failure.

Then I saw this, and the light in my head went on:



That is how CO2 exists in the tank at various pH levels. And plants love carbonic acid (H2CO3) much more than the other forms.

Before I started using pressurized CO2, I had an underpowered DIY setup. And because of my 8°KH, I was also adding HCl to bring my pH to 7.0 since the DIY CO2 wouldn't do it alone.

When I installed pressurized CO2, I did a 50% water change that removed some of the HCl, but not all. The rest was eventually removed by weekly water changes - and I realized its removal coincided with the elimination of pearling.

So I added HCl again and BAM! My plants start pearling again, and growing a lot faster too. Now I'm just trying to figure what the optimum level is.

If you view premixing some cheap chemicals and periodically putting them in your tank to greatly benefit your plants as a "big exercise for very little benefit", you'd better stop using ferts.
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post #11 of 21 (permalink) Old 02-17-2010, 05:16 AM
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Plants actually like carbon dioxide better than any other form of carbon, or at least as well as carbonic acid. That's why the CO2 mist system is so effective - it puts gaseous CO2 right on the leaf surfaces where it can be absorbed as a gas.

I'm curious about what you discovered with your tank. I can't explain it, but I hope Tom Barr will see this and offer an explanation.

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post #12 of 21 (permalink) Old 02-17-2010, 06:58 AM Thread Starter
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Plants actually like carbon dioxide better than any other form of carbon, or at least as well as carbonic acid. That's why the CO2 mist system is so effective - it puts gaseous CO2 right on the leaf surfaces where it can be absorbed as a gas.
Ooo! I forgot about that. But wouldn't it dissolve at some point into the water inside the plant, lowering its pH and forming carbonic acid? Same effect as what I'm playing with, but works regardless of tank pH.

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I'm curious about what you discovered with your tank. I can't explain it, but I hope Tom Barr will see this and offer an explanation.
It was a discovery for me, but not new in the hobby. Wllbldrco recently posted that chart and the other info on which I based this experiment. As long as the pH is low enough to shift the balance to carbonic acid, the plants benefit. Most people do that by using RO/DI water, whether they understand the reasons behind it or not. I simply substituted a different method for reducing pH. If I had RO/DI water, I'd use it instead.
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post #13 of 21 (permalink) Old 02-17-2010, 05:06 PM
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Quote:
Originally Posted by DarkCobra View Post
Ooo! I forgot about that. But wouldn't it dissolve at some point into the water inside the plant, lowering its pH and forming carbonic acid? Same effect as what I'm playing with, but works regardless of tank pH.
All biological critters and weeds use CO2[aq], even us, our lungs still have to go from CO2 [gas] to a CO2[aq] in our blood.

The insides of cells are not gas, they are liquid water.

You are simply reducing KH this way, I think RO would be a better solution than Acid for most folks. Certainly much safer, less toxic, smelly, less prone to the many risk involved with a strong acid at a high concentration.

Folks can also easily kill all their fish if not careful.
This is asking for trouble.

In theory, you can lower the KH, and yes, CO2 is given off, just like vinegar and baking soda. But how much CO2 is given off and is that really what is causing the results you see occurring?

I think the relative amount of CO2 is very small.
I think it's far more likely the issue is you are now simply comparing softer KH to harder KH.

You also have a CO2 management issue in the first place.
Plants may or may not pearl, but this does not imply they are not growing etc well or not, even so, if you have fish gasping, you have other issues, not related so much to CO2, but of O2/circulation and light intensity.

Fish respiration is a function of BOTH CO2 and O2 concentration across the gill/ More O2, the more/higher the CO2 concetration can be. If the O2 is low, then even a little CO2 addition will send fish gasping to the surface.

I often suggest good current for the fish health and well being, most all advice does. Plant aquarist sometimes reduce the flow to save their CO2, bad idea.

Some start off with excellent flow when their tanks are hardly planted and they are waiting for it to fill in. By then, 2-6 months later, the weed choked tank has virtually no flow comparatively. While plant O2 production can counter act this some, often it does not.

So more flow and surface movement is required to keep up, or more pruning, or you can also use less light which will reduce the demand for CO2.

So less in that case is better as far as management of CO2.
More light= more demand for CO2.

So you can manage this several ways, RO, peat, strong acids, reduced light intensity/duration, better flow/current, surface movement etc.

Given the trade offs and fish health, I'd not use strong acids.
Okay to add a few mls to a trace water mix of CMS+B etc, but not much else really.

Quote:
It was a discovery for me, but not new in the hobby. Wllbldrco recently posted that chart and the other info on which I based this experiment. As long as the pH is low enough to shift the balance to carbonic acid, the plants benefit. Most people do that by using RO/DI water, whether they understand the reasons behind it or not. I simply substituted a different method for reducing pH. If I had RO/DI water, I'd use it instead.
I think if you want more CO2 for the plants, then add more CO2, it's much simpler than what you are thinking it is.

If all we had to do was reduce the KH, and then CO2 would be a snap, everyone would have long done this. It's fairly well known that at low KH's, a number of species do well and most plants do better overall as long as we add CO2 gas.

However, this has nothing to do with adding HCL and releasing CO2 for the plants that way.

The amount of CO2 released and the time is stays in solution is brief.
And if you add too much HCL and there's no KH left after, then you really knock the pH way down and kill your fish since now there's no buffer to address this strong acid. Something like a weak acid will not harm fish in most cases in this case, but a strong acid will. Good luck with that.

I see burns, bad lung/nasal issues from fumes, spills, splatters, corroded spots all over the house, angry spouses, dead fish, still not addressing the root issues, many better alternatives.

Use RO if you want lower pH/KH.
Or use CO2 better and stop gassing your fish, keep the O2 up, use less light so there's less issues with CO2 demand.

My tanks use low light, pearl and no gasping fish:



Plenty of examples over long time frames.

Here's my tank from Santa Barbara tap water with a KH of 11 and Gh of 24:



Pearling is strong, there's also a lot of current.


Etc.

Work on the real issue; CO2/O2, do not avoid it.
Fish will be better off and far less risk.
Your self also

Regards,
Tom Barr




Regards,
Tom Barr
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post #14 of 21 (permalink) Old 02-17-2010, 09:07 PM
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Quote:
Originally Posted by Hoppy View Post
KH does not "mop up" CO2, and having a high KH does not cause you to have to add more CO2 to the water. All that having a high KH does is change the mix of carbonates, carbonic acid, and dissolved CO2 in the water for a given total amount of CO2 in the water. The CO2 is just as available at a KH of 6 degrees as at 2 degrees.

Well,then please help get this old wives tale out of my head..


How does it change the "MIX" ratio..This has been an old saying going back years,and now it is time to rid myself of this..If it changes the mix.how so??

Thanks,
ZEN

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post #15 of 21 (permalink) Old 02-17-2010, 09:18 PM Thread Starter
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In theory, you can lower the KH, and yes, CO2 is given off, just like vinegar and baking soda. But how much CO2 is given off and is that really what is causing the results you see occurring?
This and other statements seem to indicate you've misunderstood me.

I never claimed the improvement is a result of CO2 being released due to acid/base reaction, as seen when mixing vinegar and baking soda.

I said the improvement appears to be a result of lowered pH shifting dissolved CO2 to the carbonic acid form, which has higher bioavailability.

Quote:
Originally Posted by plantbrain View Post
And if you add too much HCL and there's no KH left after, then you really knock the pH way down and kill your fish since now there's no buffer to address this strong acid. Something like a weak acid will not harm fish in most cases in this case, but a strong acid will. Good luck with that.
People keep warning me away from HCl for this reason. I understand they're trying to help; but after hearing the same warnings dozens of times, every time I mention HCl, it seem like a knee-jerk reaction. No consideration is ever given to the specifics of my tank or my abilities.

After adjusting my pH with HCl, I've gone from 8°KH to 7°KH. There is plenty of buffering capacity left, and my pH will not suddenly or magically crash from anything less than a large overdose. Simply put, I am not stupid or careless enough to do that!

In fact, the issue of HCl use is completely irrelevant to what I'm trying to find out. I could have lowered my pH with RO/DI water, and it wouldn't have changed my question, results, or what answers would be useful to me.

When starting this topic, I seriously considered omitting the method of lowering pH, or even lying outright and saying I lowered my pH with RO/DI water, just to avoid the inevitable lectures that sidetrack the real topic.

(And Zenfish, this is why I never want the info on HCl I wrote earlier stickied. I would never hear the end of it...)

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Originally Posted by plantbrain View Post
I think if you want more CO2 for the plants, then add more CO2, it's much simpler than what you are thinking it is.
I'm not sure why you say it's that simple, when you also seem to be aware that I can't add more due to fish gasping:

Quote:
Originally Posted by plantbrain View Post
Plants may or may not pearl, but this does not imply they are not growing etc well or not, even so, if you have fish gasping, you have other issues, not related so much to CO2, but of O2/circulation and light intensity.

Fish respiration is a function of BOTH CO2 and O2 concentration across the gill/ More O2, the more/higher the CO2 concetration can be. If the O2 is low, then even a little CO2 addition will send fish gasping to the surface.
I've considered the possibility of low O2, but I think it's unlikely. I'd like a second opinion, though. Here's my tank:



46g bowfront, picture taken today after a recent heavy trim; on average there's a lot more plant mass in there. Lighting is 80W, 2x T5NO and 2x spiral fluorescents. Circulation is an Aquaclear 70 and Magnum 350 canister. Pressurized CO2 at about 60ppm per pH/KH measurement, injected directly into the Magnum which provides diffusion and a bit of CO2 mist. CO2 remains on during lights-out with an airstone providing extra O2. EI dosing slightly above recommended levels across the board.

I have played with all these parameters since I started pressurized CO2 - increased CO2 to limit, increased lights, increased ferts. And yet the biggest single improvement in plant growth occured by simply changing one thing - pH.

Quote:
Originally Posted by plantbrain View Post
Work on the real issue; CO2/O2, do not avoid it.
If there is actually an underlying issue with CO2/O2, I don't know what it is; therefore, I can't work on it.
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