Setting up a low pH tank (~6.0) - The Planted Tank Forum
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post #1 of 24 (permalink) Old 10-13-2015, 06:58 PM Thread Starter
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Setting up a low pH tank (~6.0)

Hi folks,

I'd like to set up a low pH soil based tank without running CO2.

Currently, my RO-water tanks can be nudged to 6 for a few days, but creep back above 7.5 after that time. I'm not sure if it's the plants or cap (sand in one, gravel in another), but I'm planning on testing to find out.

Any suggestions? Setting up a new one soon, and was thinking about even going no cap if I can't find one that won't buffer the pH up.

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post #2 of 24 (permalink) Old 10-14-2015, 11:38 PM
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You need sufficient acid (buffers) sources to keep the pH low, things like bog wood, peat moss, Indian almond leaves etc. Water is quite a good solvent, so if you put these things in areas with flow, they will dissolve faster and release acid faster.

pH is the equilibrium point between carbonic acid, bicarbonate and carbonate. So to shift the pH lower (equilibrium to the left) you need more acid, and to shift the pH higher (equilibrium to the right) you need more carbonate (alkaline sources).

The natural acid sources listed above will want to buffer at a low pH, so don't remove all of the carbonate sources thinking that this will help to lower pH. It will, but the equilibrium point will shift far to the left. Instead, you need to find the balance point where you have just enough carbonate sources to feed the acid sources, where the equilibrium point is at the desired pH.

An excellent source of carbonates are things like shell grit. The poor solubility of shell grit (all carbonate sources) is an advantage, since it won't all dissolve quickly, and thus provides a good stable source of carbonate. As with the acid sources, placing carbonate sources in areas of higher flow will increase the rate at which they dissolve. The higher the amount of acid in the water, the faster the shell grit will dissolve also. This helps to protect against pH crash, since as the pH lowers, the shell grit dissolves faster releasing more carbonate to offset the effects of the acid (a good thing).

A healthy supply of both acid and alkaline sources will provide stable levels of each. If you need to remove all carbonate except for one little piece of shell grit to reach the desired pH, you're probably to close to disaster, since when that one piece of shell grit dissolves, and there are no longer any carbonate sources present, pH is likely to drop very low, and very rapidly, leading to disaster. With this in mind, take things slowly and don't get overzealous about hitting a specific pH. pH is just an indicator, and the fish won't care if it's not at the optimal point, but they will care if the balance is lost and things start swinging rapidly.

Since your KH test kit is likely to give results for total alkalinity, it's useless for determining just the carbonate portion of total alkalinity. ie: It won't accurately tell you carbonate levels. With this in mind, you're going to need to use the grey matter between your ears to ensure you have a sufficient supply of carbonate.

So in summary, the safest place to start is not to remove carbonate sources, but to increase acid sources. Once you can no longer increase acid sources (for whatever reason), then start slowly reducing carbonate sources. Don't expect immediate results, add or subtract substances, then wait.

There's a good reason why people suggest to forget about targeting a specific pH.

Feel free to edit.
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post #3 of 24 (permalink) Old 10-15-2015, 04:36 AM
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What is the GH and KH of your tanks now and how are you re-mineralizing your RO water? For instance I use Equilibrium to re- mineralize my RO and it naturally buffers the PH between 7.4 and 7.8 It also does not add any KH to the water so there is very little stability to the PH which allows it to fluctuate if you do not increase the KH at least a couple degrees. I use Seachem Alkaline buffer to add KH. I suspect it may just be baking soda though. This does usually raise the PH above 8.0 however PH is not as critical in most cases. Unless you are planning on keeping exotic wild caught fish most will already be adapted to higher ph. Discus are one exception, and there are a few others but simply targeting a certain PH may be more trouble than is needed.
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post #4 of 24 (permalink) Old 10-15-2015, 02:17 PM Thread Starter
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First off, I realize this is a very specific sort of request, and that most everyone else thinks along the same lines as "don't target a particular pH". I get the reasons why. However, you try to breed otos then come and say that again lol.

Current tank params:
kH/GH<1 drop of checking solution
pH~7.5 (off low range scale, don't bother to check with high range anymore)

There's next to nobody out there that I can find who has successfully bred otos on a regular basis except for James0816 who used to post here, and Gary over at TFH.

James' parameters from here:

Temp: ~ 74
PH: ~ 7.4
NO3: ~ 40
NO2: 0
NH3: 0
GH: ~ 11
KH: ~ 6

...are pretty close (higher NO3) to what I ran for about 6 months with no luck...his pH being a little lower than my 8.

Gary's though, from:
TFH Magazine Forum ? View topic - The Otocinclus Paper [Work In Progress]

...are much closer to what they naturally live in.

His oto articles from the print magazine used to be available digitally, but not anymore. From the linked article, however:

The pH of the water can also differ from locale to locale but generally, a pH range between 5.0 and 7.8 can be handled. Anything over pH 6.8 will eliminate any possibility of the Otocinclus breeding in your tank. I€™ve kept Otocinclus vestitus in a pH of 5.6 without any issue. Once again, proper acclimatization is the key.

I€™ve never really measured for dKH or anything outside the normal testing kit ranges. Otocinclus prefer acid, soft water. The addition of Peat granules (in the filter), Peat Moss as an initial layer (under the substrate), tannins (driftwood) and Black water / Amazon Rain extract goes a long way with Otocinclus. The softer the water, the more willing they are for breeding, but that is a later chapter.

My tap water is very, very hard, so I use RO. If I add any Equilibrium whatsoever, I get TDS way above anything James reported. I also get a pH that starts at above 7.

Using straight RO for the last couple of months, I've added (I think) a 1/4 tsp measure of acid buffer to 5 gallons of weekly change water into 2 20L tanks. I drip it very slowly over about an hour or so.

That drops the tank pH down to about 6 or so, and over the next three days it creeps back up over the top end of the low range test (7.5+). TDS is about 50 or so, both have peat and manzanita wood. One has sand, the other sand and gravel mix, both have the same pH creep upward.

All I can think is that the substrate is buffering the pH upwards. Far from crashing downward, as is always the warning, mine still creeps up. Hence the question posted.

To test, I'm planning on running a tank with soil but no cap, or an extremely inert cap if I can find one. I like the look of Home Deport play sand, but it seems to have a buffering effect.
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post #5 of 24 (permalink) Old 10-15-2015, 02:41 PM
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The issue with pH down, is simply that it is not a stable source of acid, unless you continue to add it (very) regularly. Otherwise, you add it, it drops pH from the sudden increase in acid, and then the pH climbs again with the gradual release of available carbonates.

You have a strong stable source of carbonates, since your pH will climb some time after adding acid. As I described above, reducing carbonate sources is risky, since if you deplete this carbonate source, pH will drop far and fast. You're likely to panic and add a bunch of bicarbonate to raise the pH. Or in other words, your carbonate mineral levels bounce all of the place which is not good.

A far safer solution, is to increase the acid levels with a strong stable source. pH down is strong, but not stable. Natural acid sources are stable but not strong, add more of them, and pay attention to your carbonate levels, they will drop.

If you find yourself in a situation where pH is dropping below the desired point, do not add bicarbonate. Bicarbonate is a weak buffer against a strong stable acid source. Here, bicarbonate will work like pH down, it will raise pH for some short time, after which the acid source will quickly deplete the bicarbonate (it's not stable).

Keep a supply of carbonate source handy. Carbonate is a strong stable source. It's poor solubility means that it won't bounce the mineral levels in a fast fashion, instead, it will gradually increase carbonate (mineral) levels and pH. You can also slightly reduce the level of acid sources (remove some wood, peat, whatever), but you must increase carbonate levels first. Reducing acid sources alone won't do anything (significant) to pH without a carbonate source.

Feel free to edit.

Last edited by Audionut; 10-15-2015 at 02:59 PM. Reason: Add some extra information regarding a pH crash.
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post #6 of 24 (permalink) Old 10-15-2015, 03:38 PM Thread Starter
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Sounds like time for some test setups!

I'll make up a couple of vats to play with some concepts here.

Thanks folks, will report back later.
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post #7 of 24 (permalink) Old 10-15-2015, 03:48 PM
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Check/w Dianna for her receipt for in house(DIY) organic blackwater extract.

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post #8 of 24 (permalink) Old 10-16-2015, 12:52 PM Thread Starter
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I found what I think that should be, thanks. Set up a pot of boiling peat last night, and let it cool down overnight. Should be ready to strain today, so I'll do some testing.
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post #9 of 24 (permalink) Old 10-18-2015, 10:43 PM Thread Starter
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Okay, tests are in, and I confess I got a few surprises.

Had the following setups, all starting with 12 cups of RO water, and all but the control and black water tank RO got 1/8 tsp of Seachem Acid Buffer. Only measuring on the low pH test range I have, and KH in drops because I only care about relative values.

1) control, just RO
2) 1" soil layer + acid
3) 1" soil layer, 1/2" sand + acid
4) 1/2" sand + acid
5) RO + acid
6) RO plus 3/8 tsp backwater extra from boiled peat
7) tank water from one 20L oto tank

Did these up Friday, checked today. Results are:

1) TDS 3, KH 0 drops, didn't bother checking pH
2) TDS 220, KH 2 drops, pH 7.6+
3) TDS 181, KH 3 drops, pH 7.6+
4) TDS 180, KH 2 drops, pH 6.8
5) TDS 620(!), KH 0, pH <6
6) TDS 10, KH 0, pH 6.4
7) TDS 210, KH 5, pH 7.6+

So, in a nutshell, it's not the sand making this difficult, it might be the soil. Since I need soil to grow the plants the way I like, I have to decide whether to go high tech, or I'm not getting my pH down.

Useful, though somewhat annoying. I suspect I'd rather go CO2 than lose the dirt.

Thanks folks!
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post #10 of 24 (permalink) Old 10-18-2015, 11:03 PM
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Why not just get an active substrate instead of messing with acid buffers and co2?
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post #11 of 24 (permalink) Old 10-18-2015, 11:09 PM Thread Starter
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Originally Posted by Buu View Post
Why not just get an active substrate instead of messing with acid buffers and co2?
Sorry, such as what? I always used soil for its simplicity and ease of growing plants.
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post #12 of 24 (permalink) Old 10-18-2015, 11:11 PM
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What kind of soil? Can you detail what it is, or how you treated it?

Many potting soils have some form of calcium carbonate added so the organic materials will not drop the pH too much.

Test set ups:
1) Pure peat moss substrate, RO water.
2) Peat, RO, add a pinch of Seachem Equilibrium to get GH = 1-2 degrees.
3) Peat, RO, Potassium bicarbonate to get KH = 1-2 degrees.
4) Peat, RO, and both Seachem Equilibrium and potassium bicarbonate at the same rate as set up 2 & 3.
5a, b, c...) Blend peat and oyster shell grit (sold for budgies) in different ratios (I suggest more peat, less oyster shell) as a substrate.

Run the tests for at least a week to see if it is stable.
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post #13 of 24 (permalink) Old 10-18-2015, 11:52 PM Thread Starter
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I get it from here:

I used to rinse it a bunch, but found it's such a mild soil I don't bother to do anything other than pick the floaters out anymore. Plants love it. Never gives much of a spike when used with mature filters.

I can try the tests you suggest. Would swords and vals get along with a pure peat substrate?
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post #14 of 24 (permalink) Old 12-31-2015, 12:11 PM
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Did you try the peat tests?

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post #15 of 24 (permalink) Old 12-31-2015, 04:03 PM Thread Starter
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Yep, been running a pure peat substrate tank since this thread was started, actually. Ph isn't much below neutral, but it is slightly, and plants and fish haven't objected. Dosing PPS pro, the plants grow WAY better than my Walstad tank.

Going to be setting up my 90 with a peat substrate, starting today

Last edited by AdamTill; 12-31-2015 at 04:25 PM. Reason: Edit
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