Please would you help me tailor EI for low light + high nitrate tap water?

Whitebeam

Junior Poster
Aug 10, 2010
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As the title says.

I have a 90l (23.75USG) actual water volume Juwel tank running with pressurised CO2 (green drop tester with home-made 4dKH water) and two 18W T8 light tubes. My water comes out of the tap at about 25ppm nitrate, and I have a high fish-load, so I do not want to add extra nitrate (end-of-week test levels for nitrate are always between 25 and 50ppm). Without suppliments, my phosphate levels always test out at 0ppm (uncalibrated Salifert test kit) - dosing Flourish Phosphate to give 1ppm tests as 1ppm using this kit, so I have some confidence in this testing.

I have read the guidance on here that for low light, reduce the dosing to twice a week from three times. Ok so far.

The EI tables for a 20 - 40USG tank say add 1/16tsp KH2PO4. Ok with this too.

What do I do to get the K levels up where they should be however? I'm guessing that I need to add K2SO4, but how much? Should I add 1/4tsp K2SO4 in place of the recommended KNO3 dose?

Peter
 

dutchy

Plant Guru Team
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Jul 6, 2009
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A target of 20 ppm is enough. Some plants show difficiencies at less than 10 ppm K+. = 0,75 teaspoon or 0,25 tablespoon K2SO4 will give you around 23 ppm of K+. You also get some K+ form your KH2PO4 dosing but that's just a very small amount.

regards,
dutchy
 
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SuperColey1

Guru Class Expert
Feb 17, 2007
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Until last year my setup was pretty similar to yours. about 1WPG, pressurised, high plant load and heavy fish load.

I just dosed full EI (KNO3 and KH2PO4) then did a 40% W/C a couplle of times per week.

I dosed both macros and micros daily (3 x dose divided by 7 days.) I never had a problem.

Tap water here is about the 13mg/l Nitrate, 601µg/l P/l phosphorus, 3.45mg/l Potassium (No idea what the latter 2 mean, Someone else may though ;) ) .

At the end of the day you can use water changes to sort any problems out and also it was going straight into my water butts for the plants rather than the drain so it saved me using the tap water for the garden :)

Nice to see someone new that we don't need to convince to go lower with the light. lol

Regards
AC
 
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Whitebeam

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Aug 10, 2010
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dutchy;54016 said:
A target of 20 ppm is enough. Some plants show difficiencies at less than 10 ppm K+. = 0,75 teaspoon or 0,25 tablespoon K2SO4 will give you around 23 ppm of K+. You also get some K+ form your KH2PO4 dosing but that's just a very small amount.

My thanks Dutchy and SuperColey1.

Perhaps a daft question, but just checking... The 27+ppm of SO4 that would result from 0.75tsp of K2SO4 won't cause a problem to my fish or shrimps, will it? I've not read much about the effects of SO4 on a tank.

Peter
 
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SuperColey1

Guru Class Expert
Feb 17, 2007
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A zillion EI users haven't had a problem ;) (at least not a problem that they can attribute to SO4) I guess there's your answer seing as the ones with no problem prove it.

I couldn't tell you I just chucked KNO3 and KH2PO$ in on top of the tap N and P (and other things) so I never added K2SO4.

AC
 

Tom Barr

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Jan 23, 2005
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If the tap has high NO3, simple: use less/no KNO3 and add a bit more K2SO4 in place of KNO3.

Done.

This assumes the tap is actually 20-40ppm of NO3 etc and consistent throughout the year.
KH can move around, but in general, NO3 tends to be stable.
Regards,
Tom Barr