There are very few plants that prefer a low KH. These might include the tonnias and a few others. Many plants actually do better with hard water with a high KH. Some of them actually use the carbonate as a carbon source (vals & others). My tapwater is currently KH <1, GH 3 so I supplement both NaHCO3 and Seachem Equilibirum. For most species I'd guess that a KH of 6 or 8 is perfectly fine, and maybe ideal. This gives you more room to add CO2 before dropping the pH to battery acid levels.

 

...If I´m correct, plants can intake nutrients at maximum levels between pH 6.5-7.2. So if you go below 6.5 the plants can less easiliy "absorb" the nutrients. ...

I'm not too sure that this is proven. Therefore I just add more CO2 until I see good growth and little/no BBA. I have a tank that has a KH of 15 and work with other tanks that are at about 5 or 6 KH.

So I wouldn't worry about the lower pH levels with respect to nutrient uptake.

 

I keep the pH on my 75g at 6 with a KH of 5.82. There is a small pH swing of anywhere from 5.9 to 6.2 (CO2 levels of either 220 ppm or 110 ppm)depending on the time of day I take my measurements. The pH is measured with a Hanna 98129 meter and the KH is measured with a LaMotte Alkalinity kit so both should be fairly accurate.

I had some issues with phosphate buffers being added to my water supply along with my water company using calcium hydroxide to "soften" our liquid rock. Both of these seem to invalidate the pH/KH relationship in my water so I now use RO water in both of my tanks.

I can't really turn my CO2 up much more than it is now. I run it at a "stream" so it is impossible to count the bubbles and I really hate to turn it up any moe than it already is. A few others in this area use CO2 at incredibly high levels also.

 

Hydroxide alkalinity shows up in the Alaklinity test kits.
It does not tease apart the types of alkalinity(borate, carbonate, hydroxide etc). Test kits measure total alkalinity, so that is why they over estimate CO2 content.

Regards,
Tom Barr

 

Hey Tom,

The KH and pH results I posted above are after many weeks of using RO water and reconstituting it with Baking Soda and GH booster. I am assuming that the only form of KH in the tank is now provided by bicarbonates.

I still have CO2 levels in the 100-200ppm without fish stress and I still have BBA! Would you say either the Hanna meter (which calibrates correctly) or the Alkalinity kit are giving improper results?

Or could it be the very high swing in CO2 levels throughout the day. Levels are around 220ppm at lights on but drop to 100ppm 4 hours later and stay stable at this level throughout the day. I would think this would still be plenty of CO2 to not cause issues.

I really don't feel comfortable upping the CO2 any more since it is currently running at a stream I am leaning towards the big drop in the first 4 hours after light on as the culprit.

 

wow! answers from multple APC bigshots! thanks!

I know now what to do if I want to raise my KH.

@laith: a dutch guy has on his internet site graphs that shows the nutrient intake of plants at different pH values. I do not know how he obtained the data, but I don´t think he puts stuff on his site that isn´t true in his opinion. I don´t know whether I´m allowed to copy the images to APC, so I give a link instead. Unfortunately it is dutch, but I hope that you can understand.

http://members.lycos.nl/brieneoord/aqua/

on the left is a menu. you should go to "Algen & Planten" and than to "Spoorelementen 1". There you will find the graphs.

greets,

yme

 

I wish I knew Dutch!

I think I've seen similar graphs elsewhere but they were based on land plants...

I'm also guessing that he's recommending CO2 concentrations in the range of 10-20mg/l (according to the table on the same page)... too low for well lit tanks!

 

I'm also guessing that he's recommending CO2 concentrations in the range of 10-20mg/l (according to the table on the same page)... too low for well lit tanks!

yes he is! but that´s also due to his view on aquaria. He doesn´t like turbo-tanks. So he doesn´t add KNO3, H2KPO4 or whatever. He gets the NO3 from denitrification and PO4 from the fishfood. (in very very short terms spoken).

about the graphs, I will ask if they are based on aquatic plants.

greets,

yme

 

This might be useful, but not perfect.

http://babelfish.altavista.com/babelfish/trurl_pagecontent?lp=nl_en&url=http%3A%2F%2Fmembers.lycos.nl%2Fbrieneoord%2Faqua%2Fsporenelementen.html

 

They teach you this is true in agronomy 101. I have a tendency to believe it. I know agronomy is not underwater where I am from but I don't understand why it would be different.

I'm not too sure that this is proven. Therefore I just add more CO2 until I see good growth and little/no BBA. I have a tank that has a KH of 15 and work with other tanks that are at about 5 or 6 KH.

So I wouldn't worry about the lower pH levels with respect to nutrient uptake.

 

http://members.lycos.nl/brieneoord/aqua/

on the left is a menu. you should go to "Algen & Planten" and than to "Spoorelementen 1". There you will find the graphs.

greets,

yme

Oh my, these guys are so far off it's not funny.
Redfiled ratio is atomic, not mass.
16:1 is an atom ratio, not a mass ratio.............
You'd have to convert the mass so 16 atoms x 14 g/mol = 224/ 30.97 g/mol for P= 7.2:1 N by mass.

Very common mistake.
NO3: PO4 ratio for redfield: 7.2 x 62: 94.97 = 4.7 NO3O4 ratio.

So 2ppm PO4 and 10ppm NO3.

Some days folks will get it.
As far algae, they are very far off and still talking about Liebig's law of minimums. Ratios will not solve algae, simply having non limiting nutrient levels will. Ratios have not been show in agriculture research to be of any sigifincant importance as long as the plants do not run out. Having an ideal ratio might mean less fertilizers you have to buy for the farm, but the fertilizers like KNo3 are very very cheap for us.

I know why specific species grow in aquariums. They are using very general models that don't work well for the reasons they claim.

I know this because I know the algae and the reasons they grow and have done a good deal of testing to that end, it's pretty obvious they have not, other wise they would get different results and not have these same conclusions.

Regards,
Tom Barr

 

yes he is! but that´s also due to his view on aquaria. He doesn´t like turbo-tanks. So he doesn´t add KNO3, H2KPO4 or whatever. He gets the NO3 from denitrification and PO4 from the fishfood. (in very very short terms spoken).

about the graphs, I will ask if they are based on aquatic plants.

greets,

yme

Well der der der der, use less light, not less CO2, that's about as dumb as you can get.

Low light tanks do great with high CO2 and uses less electric, less initial cost for the lighting, less heat etc.

Light should be the limiting factor, a point totally lost by most aquarist and certainly these folks.

Adding enough CO2 solved many issues folks have had over the years with algae. 90-95% of all algae related issues are CO2 related.

Yet another reason to doubt both their theory and their methods. At low light....well what about high or medium light?

If you have rich cO2 for any light level, then you can apply that widely, but if you suggest minimal amounts at low light, then you walking a razor's edge with algae.

Then they think ratios and low nutrients levels will limit algae.
They need to think more about what makes a plant growth and less about algae.

The hobby is about plants after all.

If the nutrients are non limiting at maximum light levels, then it will non limiting is all cases.

Regarding pH, some nutrients are more available at different pH's, some are better at lower pH's but some are better at higher pH's, don't worry, plants can change the pH near their roots, leaves and do.

Most of the pH ranges we keep, 6.0 to 7.2 are fine.
BTW all aquatic sediments tend to neutral pH's over time.
So that is what they, the plants are adapted to.

Regards,
Tom Barr

 

hmmmm. I can only say: You made a good point!
I didn´t know redfield was based on an atom ratio. Learned again something!

I think I cannot give very much input to your reply, but it sure increases my knowledge!

greets,

yme

 

Sorry Tom, I cannot follow your calculations...

I calculated it this way:

0.16 mmol N: 0.1 mmol P (=16:1)

NO3:
0.16*14=2.44
the percentage N in NO3 is 22.6%
2.44:0.226= 9.91

PO4:
0.01*30.97=0.3097
the percentage P in PO4 is 32.6%
0.3097:0.326=0.95

This would indicate that the 16:1 atomic N ratio reflects a 10:1 NO3O4 ratio.
What is the mistake?

greets,

yme