# Potassium deficiency



## Skizhx (Oct 12, 2010)

Hi, my NPT has been running for a couple months now at least.

The plants are growing very slowly, but they're growing and spreading, which is good.

I've noticed tiny pinholes forming in mostly my Hygro polysperma, but in my Crypt. Wendtii 'green', as well as my Crypt. Pygmaea.

The tank is 10gal and has a single 15W T8 fluorescent for lighting, and sits in a fairly well windowlit room, but does not receive any direct sunlight. My substrate is miracle grow organic potting soil.

The tank is stocked with 3 guppies and 6 (7?) neon tetras, and some trumpet snails.

As this is a NPT, I do not dose any fertilizers, but do feed generously.

I'm wondering if perhaps part of the problem isn't the pothos I have growing out the top of the tank. Perhaps this plant (since it's the largest and fastest growing) is outcompeting the other plants for potassium?

I do not want to remove the pothos though, and I was wondering if anyone had any ideas to solve this without the use of ferts?

Thanks


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## HeyPK (Jan 23, 2004)

It does sound like potassium deficiency, especially if the pinholes are forming first in the older leaves. Plants can pull down the potassium level to the point where the fish are harmed. In guppies, I have seen several times that one or two white patches appear on the body, and then the fish will soon die if potassium is not added to the water. The pothos could very likely be an important contributor to the potassium deficiency. If you add some potassium salts, does that mean that your name will be stricken from the roles of NPT members? 
A natural way to add potassium would be to put a pound or two of soil in a plastic storage box, mix dried green leaves with it, let them compost for 2-3 weeks, and then extract the compost with water. Let the extract stand in a shallow dish for about a week while the soil particles settle out and then add to the aquarium.


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## Skizhx (Oct 12, 2010)

Hmmm, well if that's the case then perhaps adding some K2SO4 would be the best solution. I'll only have the tank for another couple months before I have to pack up and move all my stuff on a 3 day drive to the other side of the country.

I just wanted to see if I could do it without having to add ferts is all. For future reference mostly, I guess.

Could you perhaps provide a picture of a fish showing these symptoms of potassium deficiency for my own future reference?

I've tried googling "fish potassium deficiency" and the like, but haven't found any results. The single white patch symptom sounds similiar to something I had in my other tank which affected two smaller fish, but hasn't shown up since, and I was never able to get a diagnosis on it. Except I don't see signs of potassium deficiency in the plants, just nitrate deficiency (Since having cladophora problems in that tank, moving coming up, and a lot of work and personal stuff I need to wrap up here before I leave, I really haven't had much time or motivation to fuss over the plants too much. I've just been making sure the fish are healthy and happy as I do plan to move them with me when I go).


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## HeyPK (Jan 23, 2004)

> Could you perhaps provide a picture of a fish showing these symptoms of potassium deficiency for my own future reference?


Sorry, I never thought to take a picture. I have only seen this on guppies, but that is because guppies are my only fish. I have seen the symptoms three or four times, The patch shows up on only one or two fish at first. If I don't do anything, most of the rest of them get a patch or two, and then there is a mass die-off. If I add potassium, the patch persists for about three days and then disappears. The patch is milky white and is probably bacteria. Probably the potassium deficiency in the fish lowers its immune defenses.


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## Michael (Jul 20, 2010)

I've had similar problems with Walstad tanks set up with Miracle Grow with no other additives. You might try feeding spirulina flakes to your fish--these are reported to be high in potasium.

I started dosing K to solve the problem.


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## Skizhx (Oct 12, 2010)

That's interesting that you'd have the same experience with this soil. 

Correct me if I'm wrong thought but isn't the idea that nutrients are recycled through decomposition, so the soil is really only as good as its cation exchange capacity? So the fact that we both had this experience using this soil shouldn't really imply anything about the soil itself, but more about the food we're feeding and the type of plants we're keeping together?


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## HeyPK (Jan 23, 2004)

Fish food supplies very little potassium. It is better for supplying nitrogen, phosphorus and sulfur.


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## Michael (Jul 20, 2010)

To some extent, yes. But we don't really know the CEC for MGOC potting mix. And there may be some other factor in this soil in its submerged state that makes K less available after some period of time. The K deficiency did not show up until the tanks were over 6 months old.

I regard mineralized topsoil as a refinement of Walstad's method. MTS recipes call for some supplemental source of K, and clay to increase CEC.. I used MTS in my new tank, now 10 weeks old. We'll see if it develops K deficiency over time.

P.S. HeyPK, you hit the submit button before I did. That is interesting about K in fishfood. Do you know anything specific about spirulina?


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## HeyPK (Jan 23, 2004)

> Do you know anything specific about spirulina?


Nothing specific. it is made from dried cyanobacteria and is fairly high in protein. It does have potassium, but, if you have potassium deficient plants, I am pretty sure that feeding the fish spirulina flakes would be a rather slow way of correcting for the deficiency.


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