News From the Field:

Darkening The Waters with Botanicals – Lowering the pH
February 25, 2022

Look Ma, no Feet! – Johannes collecting at “Kali Jakorta” the ultimate blackwater creek.

Hi let me first introduce myself, I’m Gary Lange.  For almost 35 years I conducted leading edge biochemical research.  I was first at the university levels and then later with major industrial companies.  I used techniques and instruments like radio immuno-assays, ELISAs, monoclonal antibodies, HPLCs, sequencers and mass spectrometers which garnered many of their inventors Nobel Prizes.  For a hobby I kept tropical fish.  Actually my interest in tropical fish and nature came before the biochemistry bit, so I might rightly say tropical fish led me to a career in science.  That hobby after a few years led me to an extreme interest in fish that were essentially not available in the United States, those being rainbowfish.  Back in the early eighties there were only two or three species, now there are over 50 easily.  On our explorations we’ve easily discovered and brought back 15 on our own.  Others have found at least that many species.  And although I approach my hobby like most of you do, I also have that scientific experiment bent that makes me always want to know why and how, exactly , or as closely as I can.  And that’s where this story begins…


In 2017 Johannes Graf, Wim Heemskert, Marten Salossa and myself made a trip to the southern part of the Bird’s Head, in the Bintuni region.  That’s the western portion of the island of New Guinea.  In one of the very dark blackwater streams we did a little seining and managed to pull out about 20 very tiny silver looking rainbowfish.  It was super dark black water where your fingers disappeared just 2 inches below the surface.  When you look at the photo it’s like Johannes Graf had no feet!  Certainly not a fun place to collect as the mud was quite deep and slippery.  Conductivity was very low and pH was about 6 here.  It gets tough to tell exact pH though as most portable pH probes have trouble when there aren’t any ions in the water to even measure.  And tougher still to measure with liquid colorimetric methods as the water is already kind of “yellow”.  So my German and Dutch collecting friends decided to take these tiny, less than ½ inch fish home with them.   Their flight home was only 1/3 of my time spent sitting, waiting and flying so it was logical that they take them home instead of me.  We were quite surprised when they were grown as they looked extremely different than any of the other rainbowfish found in that region.  It was quite obvious by just looking at them and later via DNA analysis that they were a new species.  You can see them for yourselves by doing a google image search for Melanotaenia species “Kali Jakora”.  Now in normal times I would have picked some up a few years later and indeed I was planning on attending the rainbowfish conference in Germany in June of 2020.  Well you know how that story goes, COVID hit.  The fish were breeding for the Germans but to get viable eggs they were using rainwater, low pH and some tannin products.  This is not a normal way to breed rainbowfish!  Finally at the end of 2021 a friend arranged a shipment from Europe and these fish along with several other fantastic rainbowfish we collected in 2019 came my way. 


I was really wondering how to handle these fish.  I needed to breed them as quickly as possible.  And I didn’t want to kill them by lowering the pH in their water too quickly with muriatic Acid, that’s hydrochloric acid.  The commercial fish stuff in the stores now is sulfuric acid (car battery acid), which is not much safer.  You can get Muriatic acid at any hardware store, just wear glasses and be very careful, you can cause painful burns and blind yourself if you get it in your eyes.  Always add acid to water, never water to acid as it can pop, like adding water to a pan of hot grease and cause severe burns.  The potential problems with these acids are that you can use a little too much and then have the pH plummet to like 2.5 which is probably going to kill most fish.  But I know that tannins do provide a buffer albeit at a pH much lower than we normally see with our tap water.  If you get it right you can get things buffered at 4.5-6 without too much worry. 


So when I was asking if anyone had any techniques using botanicals or black water tonics Keith Kalinowski pm’d me that he had several different types of botanicals that he would send me to try.  Shortly afterwards he sent me a large box containing Casuarina cones from an Australian pine tree, Twister Pods, not sure what tree they are from, and Indian Almond leaves (Catappa leaves).  In the past at least for killifish I have boiled peat moss to get a lower pH but it is quite messy.  I’ve also used Black Alder cones to keep fungus away from fish eggs which also will lower the pH of the water and certainly turn it quite black.  People have also used oak leaves for this purpose.  I was going to try and keep these fish in a low ion environment like we had found them in Papua so I started off with some RO water that I made from my tap.  It’s important if you are messing with RO to have a kit that measures both KH and GH and a conductivity meter is also handy.  Most RO units only remove 85-90% of the ions in your water.  So if you start out with a 400 uS conductivity you can really expect only 40-60 uS RO water.  Depending on your starting water that can leave you either too low or still wanting to remove some ions.  Most of the problems seem to be with Calcium ions when it comes to egg fertility and hatching.  But if it’s also a pH thing I had to find a way to drop the pH safely and keep it stable.   My water company I think uses sodium hydroxide to raise the pH of our Missouri river water so that the lead pipes don’t leach into the drinking water.  That sodium hydroxide molecule seems to go right through an RO membrane though as the pH was still very high, greater than 9.5.  So onto the experiment.  I had two goals really.  The first was to see what color, how dark each botantical makes a known volume of water.  The second was to see how what pH would my water drop to after soaking in the botanicals for several days. 


So I started out with equal weights for the Casuarina cones and Twister pods, 10 grams (.35 ounces) each.  For the almond (Catappa leaves) I only used 5 grams as they were reported to be very acid producing.  I rinsed all products off in warm tap water to remove any dirt.  I know it suggests boiling before using but that would potentially lose a lot of the tannins I wanted.  I used 500 ml (17 ounces, a little over a pint) of my RO water (60 uS) to a microwave safe vessel and heated to 160 degrees F.  So I used hot water but not boiling.  This helped break down the leaves and seeds but wouldn’t necessarily be a sterile product.  At 16 hours I measured the pH of each bucket.  I also noted how dark each one had become.  The Casuarina cones were not very dark at all and the pH was 6.8.  The “Twistie pods” water was a very dark red color and had a pH of 6.7.  The Catappa leaves were somewhere in between but with a pH of 5.2, so much lower with only ½ the amount used.  As someone who photographs the fish I think even though the Casuarina cones didn’t release a lot of dark tannins they might be helpful in lowering the pH in a tank for photography.  Although the fish can live at higher pH’s it really doesn’t show it’s beautiful colors unless kept at a lower pH. 


After 48 hours I remeasured the pH of each bucket and then took a photo of them.  Boy the “Twistie pods” really had a very dark red color to them.  If you wanted really dark water this was the botanical of choice.  It’s pH was 5.7.  The pH of the Casuarina cones was 5.8 and the pH of the Catappa leaves was 4.8.  What did surprise me though was the conductivity.  Since natural black water is usually very low in conductivity I thought there wouldn’t be many ions released.  So starting with my RO conductivity of 60 uS the Twister pods went to 970 uS.  The Casuarina cones to 720 uS and the Catappa leaves were 750 uS.  I combined these waters to the tank with the fish already in 50% RO.  To totally lower the pH with only botanticals would have taken a lot of material so I helped lower the pH somewhat by adding a little vinegar, (acetic acid) which is a weak acid and not quite so dramatic of an acid.  This combination worked quite nicely and soon I was getting viable eggs.  I typically pick rainbowfish eggs and tray hatch them at 80-82F with aeration, changing the water in the tray every day.  This time I did it with low pH water with botanicals to match closely with the parent tank.  The 5.5 gallon raising tank also had the same materials.  Rainbowfish fry are tiny to begin with and these fry were even a little smaller.  Trying to find these tiny flecks of fish in a tannin stained tank was pretty much impossible.  I looked with a flashlight thru the bits of guppy grass hoping to catch some eye shine but rarely saw any.  Finally after about a week I saw enough fry swimming around to realize that the process was successful.  I’m now waiting for the adults to get bigger so that I can take a few nice pictures of my own of this brand new species of rainbowfish. 


If you have a fish species of your own that you want to lower the pH on their tank and add botanicals I would suggest going slowly and gradually.  I took several days to add RO to their tank as to not shock them.  Some of that RO was treated with botanicals and then the seeds and leaves added to the tank to leach even further.  Keep a good log and have a good pH probe so you can accurately know the pH.  Keep watching to make sure it doesn’t crash.  If you are like me and have something very precious that you can’t afford to lose perhaps think about using vinegar instead of a strong acid like sulfuric (pH down) or Muratic acid (Hydrochloric acid).  It might be safer for you and your fish.  I want to thank Keith Kalinowski of K.J.E. Aquatics again for his kind shipment of botanicals.  For more information on fishy things (not just botanicals) see his website at

Check out Keith’s Botanicals


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Casuarina vs Twistie Pods, vs Catappa (Almond) leaves – Twistie Pods are the darkest but Catappa leaves drop the pH much lower. 


Casuarina vs Twistie Pods, vs Catappa (Almond) leaves – Twistie Pods are the darkest but Catappa leaves drop the pH much lower. 

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