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Discussion Starter #1
Hi all,

I have tried searching for some info. on this but most info. seems to deal with pH not KH. Perhaps this is a stupid question but every time I test my water it seems that my KH goes down, and I don't quite understand it. What lowers your KH? I use RO water with a KH of about 0.6, then I use Kent Botanica KH+ to raise the KH to 2. My KH used to remain constant at whatever I raised it to, but recently it just goes down over a couple days time. I would like to keep my KH at no less than 2 and no more than 3.

Thanks,
Ethan
 

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This is going to be difficult because the KH is taken by plants in variable rate. More light, nutrients, and temperature pushes plants to take up more KH. You are going to be chasing the KH level every few days.

I found two possible solutions:
One is an automatic RO water flow via the tank. Hook up one extra filter between the RO line and the tank. Fill it up with dolomite sand and it will give your water constant KH , Ca and Mg. This flow will be reseting all levels back to normal. You can also use lime or coral to get KH and Ca.

Second one works if you have acid loving fish like Tetras, Altums and Discus. Let the KH drop to zero and never bother again. The pH will get stabilized at 4 to 5. Only one plant that doesn't grow without KH for me, is Echinodorus Tenellus. But the fish love it and other plants grow nice too.

Using baking soda to raise KH is not the greatest idea because the water will end up with lots of remaining Na making it difficult for plants to absorb some nutrients.

Edward
 

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Edward said:
Using baking soda to raise KH is not the greatest idea because the water will end up with lots of remaining Na making it difficult for plants to absorb some nutrients.

Edward
Edward, could you explain this a little more. I've been using baking soda for a couple years and was never aware that it could cause any problems.

Also, if doing regular water changes and using baking soda for the RO water that is replaced, how can Na build up?

Thanks
Giancarlo Podio
 

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Discussion Starter #4
So the carbonic acid that makes up the KH of the water gets taken up by the plants, and that is what lowers my KH? Am I understanding right? That is my main question...what in my tank is lowering the KH. I am happy with my current method of raising my KH with the "KH+" liquid, I just didn't know why it was going down, for some reason I thought the KH never changed.

Thanks!
 

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gpodio,

Baking soda is NaHCO3,
if Na accumulates over time then plants won't be able to take up nutrients at available low concentration levels. The nutrient dosing will have to be elevated to overcome this problem and therefore the algae grow may be also increased. Same theory applies to excessive K, Ca, ...
Na won't build up if water changes are done periodically. But then, not everyone enjoys wasting time pumping water all the time.
There are healthier alternatives to baking soda. Run your RO water over fine gravel CaHCO3 to get Ca and KH, or over dolomite CaMg(CO3)2 to get Ca, Mg and KH.

fishfry,

CO2 makes carbonic acid H2CO3 that takes pH down. Baking soda NaHCO3 makes KH and takes pH up.
Plants love Carbon, so they are looking for it in any available form. One is supplied as CO2 and one as baking soda NaHCO3. Most plants do prefer carbon from CO2 but there is always going to be some HCO3 uptake as well.

Not sure what the "KH+" liquid is made of but in most cases baking soda is used to increase the KH. Also, peat can remove KH from water, do you have any in the tank?

Edward
 

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Edward said:
gpodio,

Baking soda is NaHCO3,
if Na accumulates over time then plants won't be able to take up nutrients at available low concentration levels. The nutrient dosing will have to be elevated to overcome this problem and therefore the algae grow may be also increased. Same theory applies to excessive K, Ca, ...
Na won't build up if water changes are done periodically. But then, not everyone enjoys wasting time pumping water all the time.
There are healthier alternatives to baking soda. Run your RO water over fine gravel CaHCO3 to get Ca and KH, or over dolomite CaMg(CO3)2 to get Ca, Mg and KH.
I guess it depends on how you use baking soda in your tank. I've been using it without problems for quite some time. I think it's safe to say that if you use baking soda for your makeup water only and not to put back what the plants have removed in the existing tank water, it is impossible for Na to accumulate further than the concentration in the original makeup water. Evaporated water is replaced with pure RO/DI so again, no accumulation would occur. I can't say I've ever noticed such a drastic drop in KH from plant uptake, it's definetly not measurable in my high light tanks that receive weekly water changes and slightly apparent in my lower light tanks without CO2 and monthly water changes, but nothing big enough to require further NaHCO3 to be added to the existing water, I guess that's the big difference here, if your KH drop is big enough to require supplemental KH to existing water then you'd want to make sure your source of KH is pure. Perhaps using some crushed oyster shells in the filter would help balance things out and maintain steady KH levels between water changes.

Regards
Giancarlo Podio
 

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Ethan,

I just saw those pictures of yours in the "propagating E. cinereum" thread and it reminded me of this thread. What kind of substrate are you using? Is it Flora Base or ADA soil? I am suspecting that it is what's consuming your KH.
 

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Discussion Starter #9
Hi CS,

I am using Florabase...that is a very interesting point you raise, maybe that is what is going on... I have used Flourite in the past and never had the KH act like this. For the last couple of weeks since I have been paying closer attention to the KH my plants have started doing great! Before the KH was too low and there was hardly any co2 in the water.

-Ethan
 

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I'd bet that the Flora Base is causing the KH drop. Flora Base contains an acid buffer and it acts similarly to peat: exchanging Ca++/Mg++ ions for H+ ions that bind with the bicarbonates, thus lowering your KH (and GH).

Such a noticeable drop in KH from a non-carbonate buffer would make your CO2 calculations misleading.
 
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