Re: only male fry

[Mike & Diane Wise <apistowise@bewellnet.com>]

Dániel,

Let's see if we can explain some terms. In the US hobby hardness was 
originally measured in ppm TDS (total dissolved solids). As more German 
products and books (especially Tetra) became available, we started to 
use German & metric units more and more. Now the most common units used 
for describing hardness are the German hardness scales and metric 
conductivity measurements. Electrical conductivity does not measure 
hardness. It measures the ability of electrons to move through a 
substance (for us this is aquarium water). There is a rough correlation 
between the amount of TDS in the water and its ability to conduct 
electrons. At low levels found in freshwaters this is, as Lee mentioned 
in his earlier email, roughly between 1:1 to 1:2 (between 1µS:1 ppm to 
1µS:2 ppm TDS). Conductivity meters are less expensive to use than true 
harness test kits over the long run, so conductivity is commonly used to 
indicate hardness in freshwater aquaria.

To accurately measure harness, chemical test kits (using color changes 
or foam development) need to be used. Most aquarists use a color test 
kit. Most of these use one of the German industrial scales that measures 
in ºdGH (=deutsche Gesampt Härte/German total hardness) and ºdKH 
(=deutsche Karbonat Härte/German carbonate hardness). Total hardness 
measures dissolved compounds that are not easily removed from water. 
They are sometimes called 'permanent hardness'. Carbonate hardness 
measures dissolved compounds that more easily removed from water 
(commonly due to changes in temperature or organic consumption). These 
are sometimes called 'temporary hardness'. These usually occur in the 
form carbonate and bicarbonate ions, but other ions can also be 
included. The combination of dGH & dKH is the actual hardness of your 
water (ºdGH + ºdKH = ºdH). In freshwater aquaria 1º of German hardness 
is approximately 1.7 ppm TDS, or roughly equivalent to 1µS/cm 
conductivity. 

Your 6-7º dGH is your permanent hardness. It does not measure all of the 
hardness in your tank. It does not indicate the amount of carbonate 
hardness in your tank. Carbonate hardness, also called alkalinity, 
determines (for the most part) the ability of your water to maintain a 
stable pH  -  its buffering capacity. Your dKH can be considerably 
different from your dGH and affects your fish and plants, too. This is 
why it is important measure both.

For most 'normal' freshwater aquatic environments µS and ºdH (dGH & dKH) 
are close enough to be used interchangeably. There are some compounds 
that can be dissolved in water, but are not detected by your chemical 
hardness tests. Among these are ions like chlorides & hydroxides, and 
many dissolved organic compounds (DOCs). DOCs can adversely affect your 
fish without even being detected by a hardness test. They will measure 
on a conductivity meter, however. Aquarists who use both hardness tests 
and conductivity meters can determine DOC by comparing the differences 
between the two. Once TDS raises into the ppt (parts per thousand) 
range, like in marine and brackish waters, the values deviate more from 
each other.

As for your friend's fish, low pH and high temperatures generally lead 
to high numbers of males. Low temperatures (< 22ºC/72ºF) and high pH 
produce high numbers of females. pH values that affect sex ratios vary 
with the species and their environmental needs. Unless your friend's 
aquaria are in a cool cellar, I imagine that the temperature of the 
aquaria in the summer is closer to 28º (82ºF) where you live. If I had 
to guess, I would say that the eggs were laid in too acid water, the fry 
were raised in too warm water, and that the smaller females were 
out-competed for food and were the first to die.

Mike Wise

Dániel Gergely Faragó wrote:

> Hi,
>
> Thanks for the answers. Though I am getting a bit confused. As live in Europe TDS is not a common thing to measure. But we have gH and kH. So could you tell me if there is a correlation between dH and gH. Now I have a total hardness about 6-7? gH.
>
> Second, if I get it right the rules Mike wrote do not apply as the water's getting harder. So 7 microsiemens do not equal 7? dH (and 7? gH I suppose).
>
> And last, if the temperature is kept under 26 C, what can be the cause of having no females in the fry? (I ask this quite theoratically, as my friend keeps telling me that temperatures couldn't rise higher than 26 C, but egglaying happened in summer, and it is not easy to cool the water.)
>
> Thanks again
>
> Daniel Farag?
>  
>
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