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Re: only male fry



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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