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Discussion Starter · #1 ·
Can one overdose on K? I decided to do some searches on it and I came across a site(the Krib, I believe but I could be wrong) that said it's not really possible to overdose on K because it won't affect the plants. If that's the case then what about fish? Could that affect fish?

Just before anyone asks, no, I did not do this to any of my tanks. I do have a feeling that I under dosed though. :/

Thanks.
 

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yes, it is possible to overdose potassium. I'd have to recheck, but from what I remember it can affect the utilization of Ca/Mg and lead to signs of deficiency of these nutrients.

What is your current fert regimen? If you notice some pinholes on the leaves of the plants, that may be a K defiency. You can supplement it, but make sure you do it slowly and wait at least a couple of weeks to see if there's any effect....
 

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Discussion Starter · #3 ·
I really don't have a regimen because my tank is an El Natural. A few months ago, I had noticed pinholes forming in my Crypt but at first, I thought it was the start of Crypt rot but it was very slow so after doing some research, I found out that it's from a K deficiency. Some of my H. polysperma have some pinholes in it as well.

It's been almost a month since I dosed the tank with KNO3 but I didn't use the full amount that was suggested to me(the amount I used was about 1/16 tsp that gave me 10ppm of nitrate). At the time, the plants were also showing signs of a nitrogen deficiency since my nitrates were at zero and have been that way for almost a year until I dosed the tank.

The plants have recovered from that but I do still have pinholes forming(although not as much as before) so about a week or so ago, I had gotten some K2SO4 and added slightly less then 1/8 tsp.

Do you think too much has been added? My plants have grown more since adding both potassiums to the tank.
 

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Out of curiosity, how much light do you have on the tank?

As for the amount of potassium you're adding - how big is your tank?
 

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Discussion Starter · #5 ·
Out of curiosity, how much light do you have on the tank?

As for the amount of potassium you're adding - how big is your tank?
I knew I was forgetting to add info in that last post.:mad: Sorry about that.

I have a 10 gallon tank and I use two 10 watt CFL bulbs that I leave on for 10 hours every day and on most days through the Spring and Summer, the tank gets about 1-1.5 hours of morning sunlight as well.

I use the Dutch Nutrient Formula fertilizers from Homegrown Hydroponics if that's of any help.(I only have the K2SO4 and KNO3.)
 

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that's ~ 9ppm of potassium - that should be fine for now. Do you plan on dosing nitrate and potassium regularly? if so how often?
 

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Discussion Starter · #7 ·
that's ~ 9ppm of potassium - that should be fine for now. Do you plan on dosing nitrate and potassium regularly? if so how often?
I've read that potassium levels should be anywhere from 10-25ppm. Would 9ppm be enough to stop the deficiency in my plants?

I have considered dosing regularly to prevent these deficiencies from coming back. I was thinking about dosing the K2SO4 once a month and the KNO3 will depend on how long it takes the plants to use up the nitrate. It's almost been a month since I last dosed the tank with the KNO3 and my nitrate reading(I tested it a few days ago) was around 7-8ppm. How does this sound to you?
 

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I forget that you don't usually fertilize Potassium in your tank (through nitrate and phosphate). Personally, things run better for me if I dose smaller amounts more frequently. But I've never had to dose (so far) a soil-based tank.


If you would like a suggestion, I would try dosing 1/8 tsp of potassium sulfate and 1/16 potassium nitrate every 2 weeks and recheck your nitrate levels (provided that your test kit has been calibrated). That increases your nitrate by 5ppm and your potassium by 12ppm. Keep us updated on the results :) I would look to see you're getting more growth than pre-dosing and little algae outbreaks, with the nitrate levels being stable (~ 10ppm).
 

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Discussion Starter · #9 ·
Thank you for the suggestion. :) When it comes to things like this, I'm thankful for the help!

I have no problems dosing the potassium sulfate every two weeks but I'm not sure I'd want to do that with the potassium nitrate. At least not until the end of summer. In our city, there are several underground sources that we get our water from. Once section of the city might have a pH of 7.0 whereas our area is at 7.8. Normally, our water would have zero nitrates but because of the construction that going on on our street(it won't be completed until the end of summer), we are getting our water from a different area and that water has about 7-8ppm of nitrate in it. I think that's why my nitrate reading isn't going down quickly because whenever I top up the tank, the nitrates are being added back into it.

Because of this, should I still add the potassium nitrate every two weeks or should I just wait?
 

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do you do any water changes or just top offs?

If you do water changes 1-2x/month dosing 10ppm (i.e. 1/8 tsp) of potassium sulfate every 2 weeks shouldn't be a problem. If you don't then 1/16th would be a safer number and increase in 4 weeks if you still see signs of defiency......at least that's how I would approach it :)
 

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Discussion Starter · #11 ·
do you do any water changes or just top offs?

If you do water changes 1-2x/month dosing 10ppm (i.e. 1/8 tsp) of potassium sulfate every 2 weeks shouldn't be a problem. If you don't then 1/16th would be a safer number and increase in 4 weeks if you still see signs of defiency......at least that's how I would approach it :)
I only top off the tank but I soon will be doing a water change so I can remove some of the mulm that has built up on the gravel.

I think I'll just stick with trying 1/16 for now like you suggested. If I don't see improvements, I'll up the dosage. :) I don't want to take the chance of adding to much to the tank.

I do have a question about potassium nitrate. A friend told me that when he doses his 20 gal, 1/4 gives him 10ppm of nitrate so he suggested that I try 1/8 so I would end up with 10ppm. When I had first dosed the tank, I was nervous about adding too much so I had added about 1/16(or slightly more) to my 10 and it gave me 10ppm. Whenever I use one of the online fertilizer calculators, it says that it should've given me 5ppm and not 10. Could the fertilizer that I'm using be more concentrated?
 

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you may be adding 5ppm nitrate, but there is still nitrate in your tank - possibly changing your reading from the tank. The other possible cause is the nitrate kit itself being off.....

That's a little more plausible than the nitrate being more concentrated (especially if you're using a 'dry' fert like straight potassium nitrate)
 

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Discussion Starter · #13 ·
First off, I just want to thank you for sticking with me through all of this! I never thought I'd have to add ferts to my tanks until my plants started showing signs of a deficiency.

I'll take a sample of the water to a LFS to see if the nitrate results are the same. I've had the test kit(Freshwater Master Test kit from API) for over a year so it's very possible that it's not accurate anymore. Once I get it tested, I'll know for sure if my test kit is off but until then, I'll dose the potassium sulfate every two weeks.:)

Just out of curiosity, what exactly is a "lockup"? Is that what you mentioned before about excess K utilizing calcium and magnesium(for example) or is it something different?
 

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no problem, just make sure you update us on the progress in the next few weeks :)

as a 'lockup' i'm not sure what that refers to - can you point to a source? It may be the process where excess of one nutrient inhibits the use of another.....
 

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Discussion Starter · #15 · (Edited)
Will do. :) I had added my first dose of the potassium sulfate on the 15th of this month so should I wait until next week to add my next dose or should I add it either today or tomorrow and then redose every two weeks from there? I'm also going to get my water tested today so I'll post the nitrate results later on.

If you look at the section that tells about calcium deficiencies at the bottom of the page on this link, you'll see where it says 'lockup'. Perhaps something like this only happens in extreme cases.
 

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I would go ahead and dose next week for a 2 week interval.

Yes, from what I gather, 'lockup' refers to the iniability to utilize nutrients as I mentioned above. I think the levels have to be relatively high to get those types of problems in your tank.
 

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Great, good luck! If you have any other questions and I miss this thread feel free to pm me :)
 
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