It has over-eaten!

The Chaca is swimming around the tank (without taking cover in the ground as would be its usual daytime behaviour), and showing occasional signs of retching.
His belly has taken the shape of an extremely large ball – it has quite obviously over-eaten. I’m sitting by the tank anxiously – after all, two of my Mottled Whiptailed Banjo catfish (Platystacus cotylephorus) died of over-eating.
However, two hours later it had calmed down and buried itself into the ground again.

It obviously eats if it gets the chance to do so and then has digestive problems if it was too much and the food bloats during the digestive process.

I read it here or there before, but never believed it. Today I found out for myself:

The Chaca chaca is said to be able to secrete certain substances that lower the pH level to a considerable extent.

Today, after it had been quite busy in the aquarium, I had a go at measuring – the pH level had dropped from 7.0 to 5.5! Amazing.....how does it do it and why? I have another two equally sized tanks with Farlowellas, Rineloricarias and Corydoras seussi connected to the same water.

All the tanks show pH 5.5, gH 11, kH 3 and nitrite=0, nitrate=10

Now, let’s consider the following: on the one hand, this is an easy way of lowering the pH level without having to use alder cones or peat or whatever – all I’d have to do is stock the other tanks accordingly. On the other hand, it’s not a good idea to keep the Malawi meals in its tank for longer periods of time.

What might this sudden change of pH (no matter whether up or down) cause? For now, I changed the water and am back at pH 7. None of the fishes shows any particular reaction.

How and why does a predatory fish do this? Could it simply be an increased excretion of uric acid caused by an intensified metabolism? But why is the nitrite level at zero then? What use is it all to the Chaca, especially with respect to the fact that it doesn’t normally live in pH 5.5 surroundings. Possibly acidifying the environment with a specific effect on potential prey fish, an acidification which can only briefly be registered in flowing waters?

What I need to measure now is the period of time within which the Chaca managed to produce this acidification – all the tanks connected to its circuit contain a total of 360 litres (gross).

Two days later the pH level has already dropped to 6.5 from 7 – no further intake of food on the side of the Chaca, it is still digesting.

Today’s measuring results: kH 2, pH 5.5
Via the Internet I made contact with a Chaca owner who lives in New York and spends a lot of his holidays in Bangladesh where his parents come from. That’s where he hears some stories about the Chaca. They say that it is supposed to be able to secrete poison, for example. He himself has been keeping a Chaca bakanensis for quite some time now and is able to confirm the decrease in pH which he compensates for with baking soda. His attention had been drawn to this particular ability of the Chaca - which, to my knowledge, has been described nowhere else up to now - by the fact that a feeder goldfish which had only just been put into the Chaca’s tank died within seconds. He thereupon examined the water values.

The Chaca does not produce any solid metabolic end products; it digests everything very thoroughly and excretes fluids only, but what kind of fluids they are!

Water values compared to Chaca water
My tap water: (always)
gH 16
kH 10
pH 7,5

Normal aquariums: (after a change of water)
gH 14
kH 4
pH 7

Chaca aquarium: (7 days after a change of water)
gH 11
kH 2
pH 6 - 5,5

Acidification of the water (approx. 300 litres in 7 days)






For a more precise analysis I sent a sample of the water from the Chaca tank to a laboratory and received the following measured values:
4,26 (!)

731 µS/cm


no traces (!)

0,44 mg/L

11,3 mg/L

0,267 mg/L

0,214 mg/L

218 (!) mg/L

TOC (Total Organic Carbon) (Im LW ist der bei <3 ppm)
89.5 ppm (in tap water TOC is at <3 ppm)

To rule out any doubts:

Among my 12 aquariums I’ve got two towers of three aquariums in the cellar, the water circuits of which each run via a fourth filter tank.

To the left then, there are three tanks with Rineloricaria and Farlowella offspring at 26° C in tap water (see values shown above).

To the right there are also three tanks with Hemiloricaria and Farlowella offspring and one Chaca chaca in the bottom tank plus a P. gibbiceps of 15 cm and a few feeder fishes (Tilapia, 5 cm) from time to time.

The water values on the left-hand side are stable, but those on the right-hand side have been fluctuating within seven days as stated in the above shown table since I got the Chaca.

I believe that other factors apart from the Chaca chaca’s digestion can be ruled out, and I have the confirmation of the phenomenon by another Chaca-keeper.

Otherwise the Chaca requires very little attention or care. It lets me transfer it from one tank to another by hand without showing any resistance – even a phlegmatic banjo catfish wriggles around more than that! And concerning all those tiny little teeth in the top and bottom row of its large mouth: they sure look dangerous, but they’re only little bits of skin!