Basic Water Chemistry - making water from tap + RODI - The Planted Tank Forum
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post #1 of 18 (permalink) Old 07-23-2014, 10:28 PM Thread Starter
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Basic Water Chemistry - making water from tap + RODI

Setting aside for the moment whether I really need to, I've bought a RODI system and want to bring down the Ph of the tank from the tap water I am using.

Tap water chemistry:

ph: 8.4 - 8.6 (or maybe higher, sometimes seems off the chart)
KH: 4
GH: 8
Phospate: 0.15

Current tank chemistry (after cycle, after a fair amount of vinegar, some HCL, and and one 25% water change with RODI water):

ph: 7.8
KH: 6.5
GH 11
Phospate: 0.15
Ammonia/Nitrite: 0
Nitrate: 5 (maybe a bit higher not quite 10)

What I'm looking for is a target, and which items are most important. I think I want to aim for somewhere in the low 7's for ph.

I think I want to do this by mixing tap water (primed of course) with RODI water to see how close I get. I'm game to remineralize RODI if necessary.

I think what I need to do is aim at a lower KH, to match a lower PH, but I'm having trouble coming up with a correct target, especially a target for water to add (as if I understand KH rises over time in a cycled tank?)

In other words, I think what I do NOT want to do is just mix the two waters to a proportion that yields the right PH, but rather mix tap and RODI to a specific HK target so it can sustain an appropriate PH.

Is that correct?

Is there some guidance out there for a planted tank (low tech) for what optimal targets are?

Yes -- the fish are alive, and I could probably live with tap PH in the high 8's but everything I read steers me toward it being a healthier group in the low 7's rather than mid-high 8's.

Am I on the right track? Any quantitative advice?

Tank details:

45G, cycled as of a week ago, 78 degrees; lightly planted with Jungle Val mostly), Crypt Wendtii (one clump), Anubis (one clump), amazon sword (recent addition, one plant with 11 leaves). Plants are healthy and growing nicely.

Fertilize with 2 root tabs (Crypt and Sword), Flourish Comprehensive 1 cap per week, Flourish Excel 1 cap twice a week, Flourish Iron 1 cap per week.

Substrate ecco-complete + gravel (about half and half).

Lit with Current Satellite LED+ about 16" of water to the bottom, 2 x 4 hours daily.

Stock: One raphael stripped catfish, 5 x Serpae Tetra, 2 x Congo tetra, 2 x juvenile angelfish (koi), 4 ramshorn snails, 10 ghost shrimp. All seem happy and healthy.
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post #2 of 18 (permalink) Old 07-24-2014, 12:08 AM Thread Starter
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Let me elaborate (on a too long question already, sorry).

I just mixed up a solution of 2 parts RODI and 1 part tap water (PH about 8.5).

I added a drop of prime for realism, let it sit a while after stirring thoroughly.

The PH measures 8.0. I was hoping for a lot lower. But the 2:1 ratio takes KH to about 1.3, which is perhaps too low already.

This is why I'm stalled a bit on what to focus on in building the ratio and/or supplements.
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post #3 of 18 (permalink) Old 07-24-2014, 12:21 AM
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The water company often adds something to keep the pH up. This means that the tap water KH (4 degrees, per your first post) ought to stabilize the pH a lot closer to neutral, but it won't because there is something else controlling the pH.

Here is how I approach this problem:

1) Set the GH at the right value for the fish. If you are keeping soft water fish you might blend RO + tap about 50/50 to drop the GH to around 4 degrees.

2) Make the KH roughly the same as the GH. In this case, I would not worry about it. A 50/50 blend of tap + RO ought to make the KH about 2 degrees.

3) Filter the water through peat moss. This will add organic acids that many soft water fish like, and can act as an ion exchange media, perhaps removing what the water company has added.

4) Ignore the pH unless it is still way out there, impossible for the fish. Actually, most fish can handle a wider range of pH as long as the minerals are right.

Option 1:
Call the water company and find out what they are adding. Then find some way of getting it out of the water.

Option 2:
Go 100% RO and remineralize with GH booster and a carbonate source (potassium bicarbonate or sodium bicarbonate are commonly used) to suit the fish.

Option 3: Select other fish that are OK in slightly harder, alkaline water. Most community fish that have been raised in captivity for several generations will handle much wider range of conditions than their ancestors, though some can only breed in conditions pretty close to their ancestral waters.
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post #4 of 18 (permalink) Old 07-24-2014, 12:34 AM Thread Starter
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Thank you Diana. The fish are doing OK, but (whether I needed to or not) I worked pretty hard to bring it down to the 7.8 it is.

Doesn't filtering through peat put a lot of tannins in the water? And do you then remove any carbon in the filtration as well?

I'm leaning a bit toward Option #2 if that's really as easy as it looks. It sounds like you add alkalinity buffer to get maybe 3-4 KH, then a specific ratio of acid buffer, and something like Seachem Equilibrium for trace elements.

In a rough guestimate it looks like for $20-30/year I could nail whatever ph I want, adjusting slowly of course as I change?

As to option 1 - calling the water company -- don't get me started. They are pretty awful. And frankly I wouldn't believe what they told me.
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post #5 of 18 (permalink) Old 07-26-2014, 07:29 PM Thread Starter
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OK, not a lot of RODI users here perhaps? Any other advice?

In the hope of someone either correcting me, or if this works well helping someone else, here's what I decided.

I decided to use RODI alone, no tap. Since I got an RODI filter, there's no real benefit to mixing, and a lot of unknowns as to how to "fix" it in mixtures.

I decided to use Seachem as follows:

Equilibrium: 1 teaspon per 5 gallon bucket, aiming for about 5 GH.
Alkalinity buffer: 1/2 teaspoon per 5 gallon, aiming at about 6 KH
Acid buffer: 1/4 teaspoon, aiming for resulting ph of 7.0

My first batch (two buckets) came out a bit acidic with this (6.8 in one, 6.6 in the other) but I am still unclear whether the test kits are accurate at that point (i.e. right after mixing).

After replacing 10 G in my 45 G tank, starting at 7.8 ph, I ended up with... well, 7.8 or maybe just a tiny bit less. And I actually think that's correct in a perverse sort of way. From what I read (though no one quite says this), I think to average PH you need to do a weighted average of the exponential, i.e.

log10((35*10^7.8 + 10*10^7.0)/45) = 7.71 ph

Which is probably about where I landed. That means if I really had 7.0 water (despite measurement, depending on seachem) then it will take a bit over a dozen water changes to get near 7.0 (mathematically at 12 changes it hits 7.1).

I am not at all sure of the theory above (I am sure of the math, just not if it applies). But 1 data point aligns.

This would imply if I want to get near 7.0 in fewer changes I need to start with a more base change water. If I took it all the way to 6.0 for example, the math says I need about 6-7 water changes.

Again, not sure I have the right chemistry theory -- do I? I've seen a dozen articles saying "you can't average water change ph and predict the new ph" but I've seen no articles telling you the right math, so I'm guessing.

My plan is decrease the ph of the new water nearer 6.0, and see if my next change yields the calculated new PH. I may do the experiment with some aquarium water in a bucket first also. Going from 7.8 to about 7.1 (+/-) in 6 changes seems a very slow adjustment.

I welcome corrections on the basic approach (weighted average of exponential to calculate resulting mixture ph) as well as the targets of 6 KH and 5 GH for planted tank and (mostly) tetras.
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post #6 of 18 (permalink) Old 07-26-2014, 08:26 PM
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If I remember correctly, it takes fish weeks to adjust to even small changes in water chemistry, so dragging it out won't really save them much stress. If you wanted to change the pH faster, you could make larger, more frequent changes. Or you could change 90% of the water two days in a row and it would be like using the plop & drop technique. I wouldn't try to make the RO water more acidic. That just makes it more complicated and as a rule, the more complicated something is, the more likely you are to mess it up.

I think you should just adjust your RO water to whatever you want the tank to be, then follow your normal water change routine until the tank water matches the reconstituted RO. Keep it simple.


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post #7 of 18 (permalink) Old 07-27-2014, 01:55 AM Thread Starter
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Quote:
Originally Posted by Fishly View Post
I wouldn't try to make the RO water more acidic. That just makes it more complicated and as a rule, the more complicated something is, the more likely you are to mess it up.
But isn't the net effect the same, the relative addition of more and more acid buffer and less (by dilution) alkaline buffer.

I.e. (conceptually I did not do the math) adding less ph 6.0 water or more ph 7 water, if you get the ratio right, ends up with the same thing?

Or does it?
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post #8 of 18 (permalink) Old 07-27-2014, 03:40 AM
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Less complex!

1) Run RO water into bucket.
2) Add Seachem equilibrium to GH 3 German degrees of hardness.
3) Add baking soda to KH 3 German degrees of hardness.
4) Add a handful of peat moss in a nylon stocking for black water fish.
5) Stir it until the Equilibrium has dissolved. (it is hard to dissolve).
IGNORE THE PH

Make water changes such that the new GH or KH is not more than a degree or so lower than it was before. You can do a couple of these water changes each week.

If the tank needs a larger water change, then make up more water with the GH and KH matching the tank parameters and do as big a water change as you want. DOES NOT MATTER WHAT THE PH IS.

Over time the fish will adapt to the lower mineral levels, and you will be removing whatever the water company has been adding that holds the pH so high. This will take time. Let it. The fish cannot adapt to new water parameters (especially mineral levels) quickly. If it takes a month, let it.
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post #9 of 18 (permalink) Old 07-27-2014, 04:04 AM
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Hi Linwood,

I will keep this short and simple, I filled my tank about 3/4 of the way with ro water at 0ppm and ph was at about 6.8 (tap is 8.2!) so since i needed to get my gh and kh to their optimal levels and the ph up to 7 I just added a few 5 gal buckets of primed tap water and my fish and plants are thriving, The tank cycled for like a week and a half then I added substrate, then plants, and then fish. you can cycle with the substrate but mine just didnt arrive in time. Just remember dont over-complicate things, look at one parameter at a time fix it and move on to the next one. Also keep in mind its better to use your tap as a buffer than adding unnecessary chemicals.

Good Luck

Bump: oh and you should aim for between 3 and 6 with gh and kh
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post #10 of 18 (permalink) Old 07-27-2014, 01:40 PM
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Quote:
Originally Posted by fishfreak36 View Post
Also keep in mind its better to use your tap as a buffer than adding unnecessary chemicals.
I wouldn't say it's better to use the tap as a buffer since you don't know what's in your tap. The water company is already adding "unnecessary chemicals" and to mix them back into the RO kind of defeats the purpose of filtering the water. If you mix in your own buffer, you know what you're getting.

I once read a thread by a woman who didn't want to add dechlorinator because she wanted to "avoid using chemicals". That's absurd. Water is a chemical. Oxygen is a chemical. Carbon dioxide is a chemical. Vitamins and minerals are chemicals. Nitrogen, potassium, and iron are chemicals. The entire universe is made of chemicals. No chemical is inherently good or bad, only better or worse for a specific purpose.

If you need calcium, add calcium. It's not an unnecessary chemical if you need it. (Duh.) The "unnecessary chemicals" you need to worry about are things like lead, copper, chlorine, chloramine, phosphate, nitrate, ammonia, fluoride, pesticide residue, and anything else that makes it into your local water supply. If they don't serve your purpose and are harmful to your fish, remove them and replace them with something better.


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post #11 of 18 (permalink) Old 07-27-2014, 02:10 PM
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Quote:
... unnecessary chemicals ...
But we are telling the OP to add the necessary chemicals.
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post #12 of 18 (permalink) Old 07-27-2014, 02:16 PM Thread Starter
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Thanks, Fishly, that is exactly how I was thinking -- if I'm going to the trouble of RODI water I might as well treat it as a blank slate and put in what I need. I come from an engineering background, and do realize sometimes that means I try to solve a problem that isn't a problem, but in this case it just seems simpler.

Quote:
Originally Posted by Diana View Post
Less complex!

... etc.
5) Stir it until the Equilibrium has dissolved. (it is hard to dissolve).
....
IGNORE THE PH

...
Over time the fish will adapt to the lower mineral levels, and you will be removing whatever the water company has been adding that holds the pH so high. This will take time. Let it. The fish cannot adapt to new water parameters (especially mineral levels) quickly. If it takes a month, let it.
Well, my concern is without a bit of bump on the acid buffer side it's going to take much longer than that. Maybe I'm wrong, but I am not doing water changes very often -- my bio load is low (though growing a bit, literally), but the plants seem to be slowing the nitrate rise. I am actually down at about 5ppm with the last 25% water change, which is only the second in 7 weeks. If my math is right unless I put the water I add more acidic, it will be a year before it gets in the low 7's.

Or... I do more WC's than needed, but wiping out almost all nitrates -- won't that be bad for the plants?

What I'm mixing is almost identical to what you suggest, thanks for that. I am just using the commercial acid buffer rather than that you get naturally from peat.

What I'm confused by is without something quantitative, how do you know how much peat... what is going to eventually drive your recipe toward a specific ph? Are you saying working the alkaline buffer down to a target KH will eventually just naturally end up with the right pH?

More concisely -- what keeps this process from over-shooting and ending up at pH 6? Or under-shooting and hanging in the high 7's?

Or are you saying just now and forever more ignore the ph?

PS. Thanks for the tip on Equilibrium, I had some (I thought) precipitate in the bottom of the buckets, and wondered about it, but didn't think too much. I bet I didn't dissolve it well. Is it better perhaps to add that directly to the tank after the water to be sure it all ends up there?

Bump:
Quote:
Originally Posted by Diana View Post
But we are telling the OP to add the necessary chemicals.
Yeah, "Chemical" and "Natural" and even "organic" have taken on a life of their own, and meanings that really are not there. I hate seeing products advertised as "containing only natural ingredients". As though they might contain isotopes manufactured in accelerators that do not occur in nature.

After all, ricin can be made from "natural" casterberry beans, arsenic is naturally in many fruits, and radon comes up naturally from the ground.

Marketing has deluded us into thinking that something is bad if it comes from a lab, and good if it comes from a tree, and while there's probably more bad from labs than bad from trees -- we mustn't fall for the marketing lines, but read the ingredients and whatever else we can.

I don't, for example, object to peat as opposed to acid buffer -- I just feel obligated to measure it. Maybe once I've done aquariums for a lot longer my need to measure will abate. Right now I'm (knowingly) going overboard a bit on testing and quantitative approaches, as that's my comfort zone.
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post #13 of 18 (permalink) Old 07-27-2014, 03:06 PM
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Well, I am not saying that you start with one method and forever and ever repeat that one recipe, never testing. I am saying that the basic concept of working with reconstituted RO is the way to go to get the result you want. You gotta start somewhere. I targeted the values (3 degrees) based on your fish list (Angels, most Tetras are soft water fish).
If, as you go along, you find it not working, then adjust as needed with just this one rule:

The net change after any one water change should reduce the hardness no more than 10%. So, if the GH was 10 degrees before the water change, then it should end up at 9 degrees after the water change. (If you have a meter, then go by the TDS- total dissolved solids)
If you do the math on the water changes, doing two of this type each week, it may take a month to get within your target. That is just fine.

The volume of water you actually change is based on two things:
If you add pure RO to the tank to refill, you will not be able to do a large water change before you hit that '10% reduction'. This means you are not removing much water from the tank, and whatever the water company has added will still be there, controlling the pH.
If your new water is exactly 10% softer than the existing water in the tank then you could do a 100% water change. The fish are OK with this (usually- I have done this).
This would remove almost all the stuff the water company was adding, except the small amount that lingers in the water film on all the surfaces. Obviously you would then have to dose some fertilizers to maintain the right N, P, K and traces levels for the plants.

So here is the simpicity, made just a bit more complex:

1) Run RO water into bucket. Put as much water in here as you want to do of a water change
2) Add Seachem equilibrium to GH 3 German degrees of hardness. Sub: Any calculated value such that the water change will net not more than 10% reduction in this value.
3) Add baking soda to KH 3 German degrees of hardness. Sub: Any calculated value such that the water change will net not more than 10% reduction in this value.
4) Add a handful of peat moss in a nylon stocking for black water fish. There are organic (definition: an acid that comes from plant material including tannic acid and its related chemicals) acids that the fish evolved with in their native streams. The fish that evolved in such water may have a slightly reduced immune system, depending on the water itself (with the organic acids) to be slightly anti-biotic (wide definition: many microorganisms, not just bacteria, do not thrive in acidic water with tannins and related materials) Since peat moss varies in the amount of these acids there is no way to quantify it. When I make a garbage can of water I use a knee-hi stocking full of peat moss and run it overnight. I can reuse the peat moss for several barrels of water, but have to steep it longer each time.
5) Stir it until the Equilibrium has dissolved. (it is hard to dissolve). (I set up a fountain pump in a garbage can of water and still have to stir up the equilibrium to get it to dissolve. Barr's GH Booster dissolves a lot easier, though I think they are the same materials)
IGNORE THE PH Reason: Many years ago when all they had to go by was the pH test, a whole method of fish keeping evolved based on the idea that fish were very sensitive to pH. In actual fact they are not. It is the mineral and salt levels that are important. Of course we now know that those mineral and salt levels often but not always control the pH. Those early fish keepers had the right concept: fish do not like changes in their water, but it is not the pH that is the major concern. They did not have tests to tell them what the mineral levels were doing, though, so could not follow things like GH, KH and TDS. They used the pH test as a substitute for all the tests we now have.

I also enjoy the testing and finding out what makes the tanks work. Go ahead and go overboard now, learn how things work. Then, when things change in the future you will have a good idea which test to use to figure out what is going on, and how to correct it.

Getting back to simplicity:
Do the largest a water change you can do to get rid of the chemical the water company added. That way your tank will respond sooner to the lower mineral levels and show a lower pH. Large water changes are just fine, as long as the mineral level does not change very much each time. 10% softer is a safe value, I have done this with some pretty sensitive fish and they were fine with it.
You are absolutely right that doing small water changes will take a long time to get rid of anything in the water. Doing larger water changes, more often will remove that substance faster.
The same formula works for stuff you want to remove (the water company additive) and for stuff you want to keep (nitrogen for the plants). If you are removing too much N, then add it back. (yup! with nasty ol' chemicals! KNO3 is the most commonly used material in planted tank as a source of N)

Bump: http://www.dhmo.org/facts.html

A link for those who are worried about nasty ol' chemicals in the aquarium and in their life.

A joke for the rest of us.
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post #14 of 18 (permalink) Old 07-27-2014, 03:26 PM Thread Starter
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Wow, Diana, thank you for taking the time, it makes a lot of sense, and I will digest.

As to the DHMO article, I had seen something years ago like it, but they have obviously done a lot more study in understanding this dangerous compound since.
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post #15 of 18 (permalink) Old 07-27-2014, 06:29 PM
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Hi reading this with great interest as I will be trying to do the same. Diana, you are awesome in your explanations, btw. I may have to get your detailed help once I start! I found a site, americanaquariumproducts.com that had a Pearson's Square calculator to calculate mixing RO and tap (I know you are using all RO, however), a buffer ratios chart showing desired pH, and possible buffer dosing methods. Is this a valid way for anyone to approach this very complicated chemistry and math test!?
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