Limestone as a buffer for R.O. water in plant tank?
- Thread starter DSenn
- Start date
The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
jsoong
Aquarium Advice Addict
The equilibrium point is a physical property of the chemical (in this case CaCO3), and you can't change that! If you let the limestone sit long enough in the water, it will reach the equilibrium pH. You can keep the system from reaching equilibrium by continuously doing water changes, but then a system not in equilibrium would NOT be stable, and you do want your pH to be stable.
The equilibrium pH is based on CaCO3 in pure water, which is what you are using. <So, no, R/O water won't change the equilibrium pH.>
If you use water with some other buffer (ie not the R/O water), then the pH varies with the ratio of the concentrations of the 2 buffers. This is a sigmoidal curve (S shape). You get 2 regions of stable pH, one at the pKa of the 1st buffer, the second at the pKa of the second buffer. The in-between is rather unstable. So unless you know what you are doing, you end up with unstable pH. An eg would be adding pH down (a 2nd buffer) to hard water (1st buffer = CaCO3). Adding a little & the pH stays at the original equilibrium point (so you see no change). But if you add more, it shifts into the in-between & your pH yo-yos all over the place.
If you want to end up with a specific pH in R/O water, you can't use the automatic limestone/cc method. You either get a buffer salt mix of the appropriate pH (eg R/O right, various chiclid salts .... etc) or you add a specific amount of baking soda to your water.
The equilibrium pH is based on CaCO3 in pure water, which is what you are using. <So, no, R/O water won't change the equilibrium pH.>
If you use water with some other buffer (ie not the R/O water), then the pH varies with the ratio of the concentrations of the 2 buffers. This is a sigmoidal curve (S shape). You get 2 regions of stable pH, one at the pKa of the 1st buffer, the second at the pKa of the second buffer. The in-between is rather unstable. So unless you know what you are doing, you end up with unstable pH. An eg would be adding pH down (a 2nd buffer) to hard water (1st buffer = CaCO3). Adding a little & the pH stays at the original equilibrium point (so you see no change). But if you add more, it shifts into the in-between & your pH yo-yos all over the place.
If you want to end up with a specific pH in R/O water, you can't use the automatic limestone/cc method. You either get a buffer salt mix of the appropriate pH (eg R/O right, various chiclid salts .... etc) or you add a specific amount of baking soda to your water.
So my pH will go to a 7.8 with the straight R.O. and Limestone. Well THAT sucks, but I was afraid of that, and that makes sense. Jsoong, maybe you can help me with this too...
Lets say my tap water has a GH of 7-8, a KH of 6-7, and a pH of 7.8. When I try to get my pH down to a 7 by mixing with my R.O., the most tap I can mix in is about 1.5-2 gallons. So I can get my pH that low, but then I have almost no GH and KH (1-2 degrees). This is driving me crazy, because I want my pH lower, but I also want some degree of Gh and KH, and I can't decide on which factors I should compromise.
I have also mixed sodium bicarb and R.O. Right to my straight R.O., but I run into the problem of my pH going too high with the Sodium BiCarb, and my R.O. Right doesn't even measure on my GH test kit, so I have been trying to find a happy medium with the tap/R.O. mix. HELP! I'm drowning!!!!
Lets say my tap water has a GH of 7-8, a KH of 6-7, and a pH of 7.8. When I try to get my pH down to a 7 by mixing with my R.O., the most tap I can mix in is about 1.5-2 gallons. So I can get my pH that low, but then I have almost no GH and KH (1-2 degrees). This is driving me crazy, because I want my pH lower, but I also want some degree of Gh and KH, and I can't decide on which factors I should compromise.
I have also mixed sodium bicarb and R.O. Right to my straight R.O., but I run into the problem of my pH going too high with the Sodium BiCarb, and my R.O. Right doesn't even measure on my GH test kit, so I have been trying to find a happy medium with the tap/R.O. mix. HELP! I'm drowning!!!!
jsoong
Aquarium Advice Addict
If I understand the KH test correctly <see comments on your other post>, then yes, you can't get neutral water pH without the low KH. <Perhaps I should be more precise: High carbonate levels are associated with high pH, in the absence of another buffer or CO2.>
However, low carbonate levels should not be equated with low buffering capacity. It is possible to use buffering systems that does not register on the KH kits, and still achieve good pH stability. There are commercial products (eg Discus buffer) that claims to do this. I have no experience with those, so you have to trust the manufacturer's claims. <Or maybe someone here use a low pH buffer?>
Anyhow, why are you trying to get the particular pH/KH/GH values in your water? Most fish can do fine in water that is stable, even when the pH is outside of the published range. <Someone here actually keep discus in hard water in the high 7's & even reported spawning.>
However, low carbonate levels should not be equated with low buffering capacity. It is possible to use buffering systems that does not register on the KH kits, and still achieve good pH stability. There are commercial products (eg Discus buffer) that claims to do this. I have no experience with those, so you have to trust the manufacturer's claims. <Or maybe someone here use a low pH buffer?>
Anyhow, why are you trying to get the particular pH/KH/GH values in your water? Most fish can do fine in water that is stable, even when the pH is outside of the published range. <Someone here actually keep discus in hard water in the high 7's & even reported spawning.>
I am sorry if I am not following all your posts on this forum, but ...
What are you trying to accomplish? What type of plants? fish? substrate?
People have kept planted tanks with pH's in the 5's (KH = 0 ).
When I was running a soft water tank, my KH was only 1 degree (pH 6.0) and I never ran into any problems.
What are you trying to accomplish? What type of plants? fish? substrate?
People have kept planted tanks with pH's in the 5's (KH = 0 ).
When I was running a soft water tank, my KH was only 1 degree (pH 6.0) and I never ran into any problems.
rkilling1-
I am simply trying to do a soft water aquarium, period. When I say soft, I am trying to get my pH in the 6.6-7 range. I am simply paranoid about this entire KH issue, because up until a while ago, I had no idea what it was (and was probably better off) and I didn't know it had a direct effect on pH. So, a lot of people say ''keep this amount of KH, keep that amount of KH to avoid pH crashes.'' I have an R.O./D.I unit, and I have been experimenting with mixing tap and R.O. to get to some 'middle ground' where I have a relatively low pH while still maintaining a little KH.
I ran into a biologist at a local petstore (yes, he is an actual biologist) and they have a plant tank running there with straight R.O., with some plump Rummy Nose swimming around. He said not to get too caught up in the KH issue, and that it is no big deal to have a low KH. So you see, it is hard to know what to do. Like I said I am trying for a middle of the road approach. Right now, I am doing a 2:1 ratio of R.O. to tap, so I have been mixing 3 gallons R.O. with about 1.5 gallons tap. This puts me around that 7.0 range (give or take) with a GH of about 3-4 and a KH of about 1. I would like to use this mixture for both a planted tank and a regular community tank.
You having done a soft water tank with low KH and being (I guess) somewhat successful with it makes me feel better
Thanks.
I am simply trying to do a soft water aquarium, period. When I say soft, I am trying to get my pH in the 6.6-7 range. I am simply paranoid about this entire KH issue, because up until a while ago, I had no idea what it was (and was probably better off) and I didn't know it had a direct effect on pH. So, a lot of people say ''keep this amount of KH, keep that amount of KH to avoid pH crashes.'' I have an R.O./D.I unit, and I have been experimenting with mixing tap and R.O. to get to some 'middle ground' where I have a relatively low pH while still maintaining a little KH.
I ran into a biologist at a local petstore (yes, he is an actual biologist) and they have a plant tank running there with straight R.O., with some plump Rummy Nose swimming around. He said not to get too caught up in the KH issue, and that it is no big deal to have a low KH. So you see, it is hard to know what to do. Like I said I am trying for a middle of the road approach. Right now, I am doing a 2:1 ratio of R.O. to tap, so I have been mixing 3 gallons R.O. with about 1.5 gallons tap. This puts me around that 7.0 range (give or take) with a GH of about 3-4 and a KH of about 1. I would like to use this mixture for both a planted tank and a regular community tank.
You having done a soft water tank with low KH and being (I guess) somewhat successful with it makes me feel better
Thanks.
Lager
Aquarium Advice Freak
Soft water means low KH and to some degree GH. The PH is incidental to that.
jsoong-
I am trying for specific levels because I am INSANE!!!!!!
No really, I don't feel far from it at this point. If you read the above post to rkilling1, I simply want to do a softer water tank, even if a lot of the sensitive fish could live in my tap water. It makes me feel better knowing I am adding some R.O. water in. My tap also has nitrates, ammonia, chlorine and god knows what else. I also feel that a pH of 7.8-8 (which is what my tap is after aeration) is just a little too high for soft water fish. Is what I am doing REALLY necessary? Probably not.
I am trying for specific levels because I am INSANE!!!!!!
No really, I don't feel far from it at this point. If you read the above post to rkilling1, I simply want to do a softer water tank, even if a lot of the sensitive fish could live in my tap water. It makes me feel better knowing I am adding some R.O. water in. My tap also has nitrates, ammonia, chlorine and god knows what else. I also feel that a pH of 7.8-8 (which is what my tap is after aeration) is just a little too high for soft water fish. Is what I am doing REALLY necessary? Probably not.
This sounds like a good set of parameters and is what I would go with based on the goals you've described.
Thanks for the help rkilling1. So, it would seem to me that if your water is buffered by carbonates only, then a 1 dKH should give you a pH of around 7. Does this sound right? I guess my real question is, how do people get their pH as low as a 5.9 (like Shelly up here). Is the difference between the 7 and 6 pH due strictly to the CO2?
My other question is, would it be more important to hold a higher KH value in a fish only aquarium or a plant aquarium? I want to use my current mixture of 3 gallons R.O./1.5 gallons tap (pH 7, KH 1, GH 3) for BOTH my fish only tank and a near future plant tank.
You guys have all been a great help. I really appreciate it. Joining a forum like this is probably one of the best things a fishthusiast could do. Yes, I just invented a word.
My other question is, would it be more important to hold a higher KH value in a fish only aquarium or a plant aquarium? I want to use my current mixture of 3 gallons R.O./1.5 gallons tap (pH 7, KH 1, GH 3) for BOTH my fish only tank and a near future plant tank.
You guys have all been a great help. I really appreciate it. Joining a forum like this is probably one of the best things a fishthusiast could do. Yes, I just invented a word.
Similar threads
