GH test kit question

[Ichthys]

I wasn't aware the API kit now has a table. Is it a unit conversion table?

I too, have never owned a TDS meter. Some very soft water fish require a minimal TDS, but I've never really kept any of them. People like @GaryE, who has kept a lot of those fish, would need one.

 

[TwoTankAmin]

Your are right about sites reporting GH. But they expect most fish keepers will not delve andy deeper and the API GH/KH kit is common. But a lot of those same sites also list KH and fish have no requirement for KH.

what happens to fish which the site says need a lowish GH but are living in water with conductivity.TDS that are higher than 18 ppm per degree of GH. Btw, I use a conversion rate of 17.8 for whatever that is worth.

This was my very first education into water parameters and I have stayed with it:

Water hardness follows the following guidelines. The unit dH means``degree hardness'', while ppm means ``parts per million'', which is roughly equivalent to mg/L in water. 1 unit dH equals 17.8 ppm CaCO3. Most test kits give the hardness in units of CaCO3; this means the hardness is equivalent to that much CaCO3 in water but does not mean it actually came from CaCO3.

General Hardness

0 - 4 dH, 0 - 70 ppm : very soft
4 - 8 dH, 70 - 140 ppm : soft
8 - 12 dH, 140 - 210 ppm : medium hard
12 - 18 dH, 210 - 320 ppm : fairly hard
18 - 30 dH, 320 - 530 ppm : hard
higher : liquid rock (Lake Malawi and Los Angeles, CA)

from https://fins.actwin.com/mirror/begin-chem.html#reference

The entire information starts here https://fins.actwin.com/aquariafaq.html
This link goes to the water chemistry sections which is very easy to understand https://fins.actwin.com/mirror/begin-chem.html
Some of the information there is a bit out of date, but for the most part and for most fish keepers it is more than adequate.

As I concluded in my long post above as that each of us has to use the testing method most appropriate to out situation.

Finally, if we go to a few different sites for information it is no uncommon to see different ranges for the desired GH in which to keep any given species of fish. For example Guppies: many sites wont give a GH range they just say they like hard water.

Seriously Fish says:
Temperature: 17 – 28 °C
pH: 7.0 – 8.5
Hardness: 143 – 536 ppm (using 17.8 conversion, the DH range is 9.7 - 30.1)
https://www.seriouslyfish.com/species/poecilia-reticulata/

The PetMd site only mentions GH or hardness when promoting the API test kit.
https://www.petmd.com/fish/guppy-fish-care-sheet

Fish base shows Freshwater; brackish; benthopelagic; pH range: 7.0 - 8.0; dh range: 9 - 19
https://www.fishbase.se/summary/Poecilia-reticulata.html

I could keep posting params from different sites, but the point is who is correct and which should we trust?

And here is a scientific study on thos issue and guppies which were being compared to Bettas

Krishnakumar, A., Patrick Anton, E.S. & Jayawardena, U.A. Water hardness influenced variations in reproductive potential of two freshwater fish species; Poecilia reticulata and Betta splendens.
BMC Res Notes 13, 542 (2020). https://doi.org/10.1186/s13104-020-05382-x

Abstract​

Objective​

Hardness of water in the form of CaCO3 affects reproductive potential in various fish species, differently. This study evaluates the effect of water hardness on growth and reproduction of two aquarium fishes, Poecilia reticulata (Ovo-viviparous sp.) and Betta splendens (Oviparous sp.) by growing them under 150 (control), 320, 540 and 900 ppm CaCO3 levels in semi natural aquaria.

Results​

Growth increased with increasing water hardness, reporting a significant progress of P. reticulata (p = 0.005) at 900 ppm. Similarly, the reproductive potential of P. reticulata was improved significantly, recording the highest fecundity (16.22 ± 3.90) and Gonadosomatic Index (GSI-2.48 ± 0.6) at 900 ppm.

from https://link.springer.com/article/10.1186/s13104-020-05382-x

900 ppm/17.8 = 50.56 dh or 900ppm/18 = 50.0 ppm.

Where one looks for the information matters in terms of what one might see.