Making Blackwater

[Shane]

This is my current blackwater maker. 10 gallon with a sponge filter filled with driftwood and leaves (oak and alder). Makes 10 gallons of this strength every week. I fill it with rainwater from my rain barrel, so the result is very, very soft acidic water I can cut with tap to get what I am after.
-Shane

[jp11biod]

Shane, how long do you leave the leaves and wood in your blackwater tank? Do you add it to a certain pH or TDS?

[TwoTankAmin]

I make black water every week for my altum angel tank. However, I use a different methodology than Shane.

I start with ro/di water which I use to mix 20 gals of changing water. My tap is pH 7.0 and 83 ppm or lower TDS. I mix about 11:9 ro/di:tap.

I then put in my digital probes which are normally on the tank and I adjust the changing water to produce the desired result in the tank. I add Kent Black Water Expert, brewed rooibos tea and usually some amount of muriatic acid to get the pH where I want it given where the tank is.

I add catappa leaves pre-soaked in ro/di to the tank and I use alder cones in a bag in filters. I also add the water I used to soak the catappas to the changing water.

I pretty much rely on the digital monitor to keep tabs on the tank and to get the desired mix for the changing water.

I am shooting for the tank to be 6.0 pH and 60 ppm TDS. Between weekly water changes the parameters tend to move up some, the pH to about 6.3 and TDs to the 70s. I should say that when I got the angels the tank was at 4.2 pH and TDS under 30 ppm. I spent 6 months gradually bringing the tank to where it now is.

[Shane]

Shane, how long do you leave the leaves and wood in your blackwater tank? Do you add it to a certain pH or TDS?

So the leaves and wood stay in the 10 gallon permanently. I add several big handfuls of leaves every month or so. I drain the tank every week and use the blackwater for water changes. I then refill it with pure rainwater and let it sit until the following week.

As I am using rainwater there is no sense (to me) to testing it as it will have no hardness and a low pH.

My tap water, from the Potomac River, ranges from pH 7.2-7.4 and 120-130 hardness depending on the season so I can pretty easily guesstimate in my head the ratios I need to mix to get what I want.

-Shane

[Shane]

Upgraded from a 10 to a 20 long blackwater maker. The look of that amber water makes me happy. The fibers on the left are palm fibers from a tree in my backyard in Nigeria. I saved a bag of them to bring back.
-Shane

[Shane]

Picked up a new pH meter and a new TDS meter and ran some tests.

Pure rain water from rain barrel pH 7.0 2ppm GH

Blackwater (rain water/ oak leaves 5 days)
pH 7.0 7ppm GH.

Straight tap water pH 7.14 162ppm GH

50/50 tap/blackwater pH 6.94 110ppm GH

Some thoughts...
I now see how the tetra fry lived in the blackwater tank. 7ppm is soft but not too atypical of many tropical bodies of water.

The leaves and other debris in the blackwater maker add some hardness (soil on leaves?)

After 5 days the blackwater maker imparts a nice color akin to weak tea, but is not actually changing the water's chemistry much. I need to leave some soak for 10 days and retest to see any difference.

I need to let some tap water sit out for 24 hours and then test. The 162ppm GH reading surprised me, but I normally test tank water. I expect aged tap to fall down to 145-155ppm which is the range of most of my aquariums.

Even a 50/50 mix of tap and blackwater only gets me down to 110ppm GH, which is still considered "moderately hard."

-Shane

[Bas Pels]

I'm surprized your rainwater is pH 7.0. As we all know, CO2 is one of the gasses in the air, and this one does dissolve rather good. CO2 is also known als carbonacid, and it does make your water tart.

Still your rainwater is pH = 7.0. I would assume something, perhaps a concrete roof dissolves a bit into the water.

With regard to 50/50 balckwater and tapwater, this is rather odd too. Conductivity ought to be the average of both sources, in this case 7 + 162 / 2 = 85

[bekateen]

With regard to 50/50 balckwater and tapwater, this is rather odd too. Conductivity ought to be the average of both sources, in this case 7 + 162 / 2 = 85

Agreed. Perhaps, @Shane, your conductivity meter needs recalibration or its accuracy declines at very low conductivity values?

Cheers, Eric

[Shane]

Great questions/observations. I'll run the tests again tomorrow. These are new meters, so part of the experiment is testing them as well as the water.
-Shane

[syno321]

Please keep us apprised of your testing results. I'm especially interested in how you rate your pH meter as it seems that I can't find a reliable one to use.

[dw1305]

Hi all,

I'm surprized your rainwater is pH 7.0. As we all know, CO2 is one of the gasses in the air, and this one does dissolve rather good. CO2 is also known als carbonacid, and it does make your water tart.

Still your rainwater is pH = 7.0. I would assume something, perhaps a concrete roof dissolves a bit into the water.

With regard to 50/50 balckwater and tapwater, this is rather odd too. Conductivity ought to be the average of both sources, in this case 7 + 162 / 2 = 85

That is what I've found as well. Our rainwater has some carbonate buffering and the pH is usually well over pH7, because of the carbonate ~ CO2 ~ pH equilibrium. The conductivity is much lower in the winter, it rains a lot here, so I assume the carbonate source is mainly dust.

For the rainwater I get 30 - 60 microS in the winter and 80 - 150 microS in the summer. Conductivity meters are usually pretty accurate, but a very small salts addition will greatly increase the conductivity so you have to be very careful about contamination.

If you want to make the standard and you can get pure NaCl? You need 0.491g (491mg) L-1 NaCl to give a <"1000 µS standard">.

I'll link in another UKAPs thread, <"TDS puzzles">, for some more discussion of conductivity standard solutions.

cheers Darrel

[brhau]

After 5 days the blackwater maker imparts a nice color akin to weak tea, but is not actually changing the water's chemistry much. I need to leave some soak for 10 days and retest to see any difference.

I've found that if I'm using leaves and alder cones, I can only move the pH lower by adding a very large mass of leaves compared to the volume of water.

My tap water is low TDS (about 50ppm) and high pH (near 7.8), and I can lower the pH effectively by running it over a peat column. When I directly add alder cones and leaves to my tanks, I find that they do not lower the pH. My thoughts here are:

1. Relatively speaking, I'm adding a very small mass of alder cones and leaves (though they do darken my water significantly).
2. I'm not removing the OH- ions. In the peat column case, I'm exchanging ions and discarding the peat when the binding sites have been exhausted. With alder cones and leaves, the OH- ions remain in the tank, so theoretically can re-exchange back into the water. (I don't know if that's actually what happens, but that's what I imagine.)

My guess in your case would be that the driftwood played a large role in acidifying the water, and it's been exhausted. I have observed that in my tanks, and switch out the driftwood once or twice a year.

For the leaves, I wonder what would happen if you kept them in a large mesh bag and measured the kinetics of the pH change over time. Curious if it drops, and then bounces back up if you leave it in (vs removing the bag).

I'm interested in the solution here, because I'd like to be able to make blackwater without using peat.

-Ben

[Shane]

The meters I bought are cheap Vivosuns $20 total for a pH and a TDS meter. At that price point I am not expecting scientific accuracy or years of use. I think for aquarium use they are working fine as seen by the below results. Also, at their cheap price point I would not be worried sick taking them on a collecting trip.

Pic below of blackwater after 7 days soaking.

Pure rain water from rain barrel
16 Jan pH 7.00 2ppm GH
18 Jan pH 6.70 2ppm GH

PH lowered as we have not had any rain for several days?

Blackwater (rain water/ oak leaves 5 days)
16 Jan pH 7.00 7ppm GH
18 Jan pH 6.08 8ppm GH

Big change here in pH (no surprise)

Straight tap water
16 Jan pH 7.14 162ppm GH
18 Jan pH 7.10 159ppm GH

50/50 tap/blackwater
16 Jan pH 6.94 110ppm GH
18 Jan pH 6.90 100ppm GH

-Shane

[TwoTankAmin]

My tap is well water. When I got into the hobby in early 2001 my tap was about 7.3 or 4 pH and the TDS were about 105+ (I did not have a TDS meter then.) some 10 years later a friend came over who did have a TDS meter and she tested my tank water at 83 ppm. That was when I bought my first digital meter, for TDS. This led to an interesting discovery. Normally, TDS were 83 ppm. However, if we got major heavy rain storms which occurred over a short time period, the TDS would drop as low as the low 50 ppm range.

As far as I can tell the major rain found its way into the underground water supply pretty fast. Thios ear has tons of rock and under more normal rain, the water in the system had time to become mineralized. But when big rains came. it was like doing a water change on the underground supply. I also believe the he population explosion which occurred in the decade after I got my first tank meant the water was spending less time underground before being used and therefore it had less time for things to dissolve in it. That caused the TDS and pH drops over the 10 years.

We have a gutterless roof which makes collecting rainwater difficult. So I have an RO/DI unit.

I find that to lower the pH from cones takes a fair number. And then they have to be replenished. I have two AC 200 filters on the Altum 55 gal. tank. I have a mesh bag into which I put 15-20 cones. I put a bag into each filter. I Target the desired pH after a WC to be 6.0 or a tad lower. Over the ensuing week it tends to rise forwards 6.5. Since my tap KH is low (between 2 and 3 dg) I am not sure this creates the rise in pH. In fact I have never figured it out. I add acid, catappa leaves, alder cones and Kent Black Water Expert as well as brewed Rooibos tea.

I target the tank to be pH 6.0 and the TDS in the 60 ppm range after water changes. I adjust the changing water accordingly. I have a gallon jug of muriatic acid to help me keep the pH in a range I desire. I cannot put my robes into the batching water until I have mixed the tap and RO/DI. my meter goes nuts when put into full RO/DI.

Once the two water are mixed I move my temp/tds and pH probes into the changing water. Then I add the rooibos and Kent. So I can see any changes from them. I then work on the tank allowing the circulation pump in the changing water to mix things well. Once they are, I will add muriatic acid to it as needed based on the readings in the tank. I change the catappas about every 2-3 weeks. I put about a dozen assorted sized leave into the tank. I rinse them in tap and then pre-soak them in RO/DI while working on the tank. I also add the leaf water to the changing water so nothing is wasted in that respect.

The most interesting part about this thread is how we all look to achieve similar type results but we follow very different paths to get there.

I would mention that when I first acquired the wild Altums, I brought them into a tank at pH 4.2 and TDS in the 20 ppm range (my monitor reports in 10 ppm increments but I also have a hand held meter which gives me more numbers. I confirmed that a 70 ppm reading of TDS meant the actual TDS were in the 60s. That works fine for me.

[syno321]

Thanks Shane

[Shane]

Placed a 15 gallon tub on the back deck filled about 1/4 with oak leaves. It was filled by rain and snow over the winter and just left alone. Holy smokes did it come out strong!

Note the two 40 breeders below after water changes today. Bottom tank got 50% (20 gal) tap. Top tank got 18 gallons tap and just 2 gallons of water from he tub! I'll bottle the remainder for future projects.

-Shane

[bekateen]

That looks very nice. Hopefully some fish go bonkers in that blackwater out of joy.

Cheers,
Eric