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Discussion Starter · #1 ·
I have a low tech 75 gallon. I seem to be having an issue with the KH dropping in the tank. My parameters are:

pH: 7
Ammonia: 0
Nitrite: 0
Nitrate: 10
GH: 10
KH: 0

I tested the KH straight out of the tap and it was 3. So something is causing the KH in the tank to drop. My pH does seem to be steady at about 7 with no apparent fluctuations.

My tank specifics are:

Substrate: Eco Complete
Ferts: Seachem plant tabs, Flourish (one capfull twice weekly), Excel (two capfulls daily)
Filtration: Aquatop CF500 with filter pads and bio media, no chemical filtration
Lighting: Finnex 24/7 running at 24/7 mode
Temp: 80

I have two pieces of wood in the tank (purchased at a LFS)
Lot of plants that seem to be growing well.

Any thoughts on what would cause the KH to drop to practically 0? I do monthly water changes at only about 25%. I keep them low as my nitrate readings are only at about 10. Should I step them up a bit?

I also heard the organics in the water could cause KH to drop. I have some Seachem Purigen on order, should be here today. If I use that could that take our enough of the organics to give the KH a boost? I also have Matrix showing up today. I was planning on putting the Matrix before the Purigen so the Matrix would have access to the organics before the Purigen removed it thereby allowing the bacteria to do their thing unhindered as I want a certain amount of nitrate as the tank is heavily planted (in theory).

Any thoughts?
 

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Similar problem for me in a 55 gallon.
Same tap in all my tanks with an inert substrate.

I attributed it to heavy plant uptake.
Dosing CaCO3 since I already had several pounds, solubility is terrible though.
CaSO4 would be a better choice for a solution.
 

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First double check that the KH is really 0. Tests are good liars. Calibrate the test with a/several known KH solutions.

Then...Some plants/microorganism can use carbonates as a source of CO2 so that is one guess. If the wood is new and big enough it would be the second guess.

However, nothing to worry about. If the values are accurate you have a good setup to grow CRS :D. And you can always increase the KH by adding CaCO3. CaSO4 will not affect the carbonate hardness. One with good solubility is sodium carbonate Na2CO3. I find KH ~3 to be a good target.
 

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Potassium bicarbonate is another good material to raise the KH.

Ditto the other suggestions:
The KH starts out low and the plants and microorganisms are using it. The small, infrequent water changes are not enough to replace it.
 

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Discussion Starter · #5 ·
If I was to place a bit of crushed coral or something similar in my canister filter would that serve the same purpose?
 

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It will basically add CaCO3. I find it harder to control the rise in KH and it takes longer to disolve. It will also raise the GH.

You can always scape using Seiryu/Ryouh stones and achieve the same results :D
 

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If I was to place a bit of crushed coral or something similar in my canister filter would that serve the same purpose?
Yes this will work.
People also place crushed coral or a saltwater substrate in a filter sock. Hob or canister.

With a pH of 7 it may take a while to raise the KH though.

Dosing something will provide immediate results.
 

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Discussion Starter · #8 ·
Yes this will work.
People also place crushed coral or a saltwater substrate in a filter sock. Hob or canister.

With a pH of 7 it may take a while to raise the KH though.

Dosing something will provide immediate results.

Thanks for the advice. I'll add some crushed coral to my canister as soon as I can get some. My local PetSmart and Petco didn't have any (except for the 20# bags). I'll run up to House of Tropicals (a locally owned store, they have pretty much everything) and get some this weekend.

I'm not going top go the route of the Seiryu stones as I already have volcanic stones and river cobbles. Another kind of stone would make things look haphazard. Maryland Guppy, looks like we're neighbors!
 
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