Need to increase KH and have a few questions - The Planted Tank Forum
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post #1 of 4 (permalink) Old 07-27-2016, 02:45 AM Thread Starter
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Need to increase KH and have a few questions

So I'm at what I hope is my final stumbling block before I go and get some actual fish for my tank. My tap water is super soft, 3* GH and 2* KH. I've added about 1/4 cup of crushed coral to the filter and 36 hours after adding, hadn't seen a change in hardness. (I'm using the API liquid tests.) I need to get some buffering going on; the tank went from 6.4 pH to 8.3 pH in about 24 hours. Not cool!

How long should I wait before adding more coral? I've heard people say you'll see the change in 24 hours, while other sources have it taking weeks to affect anything.

Also, how do you handle water changes without shocking the fish when you're using coral in the filter to increase water hardness? If there's no difference in pH between the tap water and the aquarium water, can you just add it in? What if there is a difference between the tap and aquarium?

(picture of my tank because I'm rather proud of it, for my first few fumbling attempts! The wisteria in the background has just been clipped in half and should grow up to hide the sponge pretty quickly.)
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post #2 of 4 (permalink) Old 07-27-2016, 06:12 AM
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Harry Kya

I have soft water here too.

I have used a few different methods, and I have found balance between using coral in my filters and using a kH powder effectively upping my PH to the desired level.

The coral helps stabilise the water and the kH additive helps adjust the water during a WC so the fish are not shocked.

I can happily do a 100% WC without stressed fish.

Just takes a bit to figure out what amounts of each you need.

Sent from my iPad using Tapatalk

May I ask if your tank has finished cycling?

I know the cycle itself effects PH and can cause it to fluctuate heavily....

If it's at the tail end of cycling it might take a tiny bit longer for the PH to stabilise.

I had all these same problems

Hopefully this helped a little.

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Last edited by Darkblade48; 07-28-2016 at 03:57 PM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #3 of 4 (permalink) Old 07-27-2016, 01:44 PM Thread Starter
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The tank finished cycling, yep! 2ppm ammonia turned fully into nitrates overnight. It had just finished cycling a couple days before I did the pH tests. (pH is probably something I should've kept my eye on throughout the cycle, but it doesn't seem to have hurt anything. I learned my lesson though and will keep a closer eye on pH when I've got fish! Thankfully the test is easier than the nitrate test, haha.) Even if it was just the cycle throwing the pH off, I think the KH is still a little low. I will be keeping softwater species but I do want some buffering power

I'll look into this KH powder more - what kind are you using?

Thank you for your help! It's good to hear from someone who's dealt with this first-hand.
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post #4 of 4 (permalink) Old 07-27-2016, 01:54 PM
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Baking soda works great for raising kH. Much cheaper than aquarium-specific products. If you plan to use CO2, it will react with the crushed coral, raising your GH so I'd advise just using baking soda and removing the crushed coral. I think a GH of 3 is fine - no need to raise it.


72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias

2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
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