KH/GH question
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KH/GH question

This is a discussion on KH/GH question within the Planted Tank Specific forums, part of the Aquarium Related Chat category; Hi, Just getting back into planted tanks and looking around I just wanted some clarity on gh/kh. Quick background, Used ...

  1. #1
    Forum Snooper
    Join Date
    Apr 2010
    Surrey, BC

    DefaultKH/GH question


    Just getting back into planted tanks and looking around I just wanted some clarity on gh/kh.

    Quick background,
    Used to live in Surrey, and had much larger Co2 injected, low/mid light tanks, 50% EI dosed. Water was almost 100% glacier water and thus you can almost call it distilled water... super soft. Back then I just ran a large filter bag of aragonite in the canisters and dosed approx one table spoon of equilibrium into a 75-90 gal tank every 50% water change (Weekly). Worked well for many years... so well in fact that once I got into a routine, I never went back to check the levels and have since forgot how I came up with those amounts.. hahahaha...

    So, I am now in the Township of Langley, we have a mix of well and glacier water. The water is harder here as I see the white calcium build up on all the pots, pans, etc... but test kits still show kh of 0.

    Current setup:
    20 Gallon tank, prob 15-18 gal of water it in it to account for substrate and decorations.
    Low / medium Lighted tank, all easy plants (mostly swords, from chain swords, to amazon swords). Also some money wort and cabomba in the tank.
    Gravel substrate, root tabs (jobe plant sticks + terra cotta clay balls)
    satellite plus pro running 7.5 hours @ approx 70% output.
    50% ei dosage
    50% excel dose
    Tank is approx 6 weeks old... just finished the cycle few days ago
    Stock is a few tetra and a bunch of guppies
    PH 6.6
    GH... don't know... I got ahead of myself and added some my plaster of paris into the tank before remember to test the GH..... it's cloudy right now as I wait for it to dissolve.
    ammonia 0, nitrite 0 (finally.. YAY), Nitrate 5-10

    As I'm keeping guppies this time, I was reading that I might need to up my gh and kh a bit... so.. pulled out my test kit and proceeded to check the kh. My last water change (40%) was 3 days ago and I blindly dosed 1/2 tsp of plaster of paris and 1/4 tsp of epson salt into the tank along with my macro and trace. I was surprised to see a KH of 0... big fat zero. Checked the tap water and also got a zero. At this point I was thinking that the test kit was faulty or the instructions where wrong, so I kept adding drops waiting for a colour change. 30 drops later, still all yellow.. (duh.. read the instructions).

    I then proceeded to make myself some liquid rock. huge spoon of baking soda into a cup of tap water... yes the kit is working.. blue right away.

    So few questions I have.
    1) Where is all the KH? I added the gypson 3 days ago..... 1/2 tsp into a 20 gallon should be lots... is it not?
    2) how much should I be adding to the tank to bring up the kh into a more suitable level...... I change 40% of the water every week (or that's the goal, it was every 2 days for the last few weeks as I tried to keep the levels under control during the cycle).
    3) what kh/gh should I be aiming for to keep everything stable and happy?

    Thanks in advance

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  3. #2
    Forum Newbie
    Join Date
    Jul 2016
    Vancouver, BC


    Hi Jonney,
    The reason you aren't seeing any change to the KH is that you havent added any carbonates to your water! All of the salts you have been adding are sulphate based (calcium and magnesium). The calcium and magnesium will change your GH (which measures those metals) but not your KH. KH is specifically a measure of carbonate hardness, so if you wanted to change that without changing the GH, you could add small amounts of sodium bicarbonate (baking soda) to affect the KH.

    That said, while I don't know too much about the fish you are keeping, usually fish prefer consistent parameters rather than "perfect" parameters, so be cognizant of messing around too much with your tank chemistry if it isn't necessary. Even if certain compounds don't effect the pH, GH, or KH they still contribute to things like the TDS and the overall environment your fish are in.

  4. #3
    Forum Novice troutsniffer's Avatar
    Join Date
    Dec 2015


    I have buffered substrate in a few of my tanks. My kh reads almost 0 at different times of the year and depending on how frequently I do water changes. I keep guppies in most of my tanks and they do well in the softer water. I wouldn't worry about keeping common guppies in a softer water environment. Like previously mentioned, you could add baking soda. But TBH it matters more if it's stable.

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  6. #4
    Forum Snooper
    Join Date
    Apr 2010
    Surrey, BC


    Ah, thank you for the explanation. Makes a lot more sense now.

    This is my first time keeping guppies and if they will do fine in our soft water, I am just going to "leave it". Might just add a pinch of GH booster for the plants and that's it.

    Thank you again



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