Verifying I don't need to add fertilizer... - The Planted Tank Forum
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post #1 of 4 (permalink) Old 08-05-2018, 07:04 PM Thread Starter
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Verifying I don't need to add fertilizer...

I'm an experienced fish guy (and experienced lab guy), but very new to the planted tank side of things (only about a year). I've had a number of failures where few poor unfortunate plants didn't make it, but things are going generally better now. I've got a fairly lightly planted tank (2 swords; 1 ea. crypt wendtii, parva,willisii; and a largish (30x10cm) carpet of Christmas moss), with a fairly high load of fish (~30 small tetras and a half dozen tiny peppered corys) in a 56g tank. I run what I believe is medium light (two Coralife Aqualight S LED, right at top in 24" deep tank), inject CO2 and best estimate based on kH and pH CO2 controller is I'm at around 20ppm.

I have been using the API test kit for Nitrate and Phosphates, and recently got the Seachem kits for the same to get a bit more precision.

My question -- with both kits, it is clear my numbers are pretty consistent -- 15-20 mg/L Nitrate (I believe both test NO3-), and 1.75 mg/L (1-2 on the less precise API kit) of Phosphate (again, I believe both test PO43-)

My understanding is that the goals with EI are for Nitrogen, 5-30 if using Nitrate testing, and for Phosphorus 1-2 if using Phosphate testing.

So is my bio load simply high enough that I am getting sufficient levels of both (for now) for my plants? I am currently adding the recommended bottle levels of Flourish Potassium (since I can't measure, and I'm certainly not getting it from other added ferts, since I haven't been adding) and Flourish for trace minerals.

I keep having a nagging feeling I'm reading it wrong (particularly around converting phosphate to phosphorus and nitrate to nitrogen levels) and really should be adding some Nitrogen or Phosphorus...

Plants are growing slowly (slow growers), but I have some BBA on some leaves, so as part of my "getting things right", I'm trying to verify that I am reading the dosing instructions right.

Thanks in advance for any feedback on "I'm reading it wrong" or "Sounds right"!
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post #2 of 4 (permalink) Old 08-05-2018, 07:33 PM
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Verifying I don't need to add fertilizer...

You probably have enough nitrate. You could probably use some more phosphorus and no mention of micros. How many Ppm of potassium is seachem recommending?

There is lots of conversation about organic vs inorganic nitrate and uptake by plants. In my mind 30 ppm should be plenty




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post #3 of 4 (permalink) Old 08-05-2018, 08:32 PM
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I might guess that you are doing okay but then that nagging doubt can be a bummer on taking the fun out!
So a different approach may fit into your thinking , as well as budget. Guessing here but I might guess that a bit different approach to the fert question might be a logical for a lab guy and that the finances would allow a $20-25 expense, if it saves money in the long run?
How about switching from the ready made but far more expensive liquids, order a full range set of very inexpensive dry ferts that would allow adding a touch of this or a touch of that to see what the plants think?The savings come in using your own water, rather than the expensive water which has to be shipped all round!
I find dipping a bit of dry, mixing it in my cup and pouring is a great way to gain a lot of control and flexibility with dosing. My favorite supply:
EI based NPK + CSM+B - NilocG Aquatics
This set will cover NPK as well as the micros. Figuring the amount is simple here:
Rotala Butterfly | Planted Aquarium Nutrient Dosing Calculator

Final is that you don't have those nagging thoughts as you can try it and see how it goes!
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post #4 of 4 (permalink) Old 08-05-2018, 08:54 PM Thread Starter
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Plain Flourish (i.e., just the micros) at 5ml twice per week.

For the Potassium, I use 2 caps twice a week, which supposedly raises it by 2-3mg/L (so it says 10ml raises 500L by ~2.5mg/L, so .02ml raises 1 liter by 2.5mg/L, .02ml contains 2.5mg, so I think I am dosing 1250mg in my 56 gallon tank twice a week)... I actually can't find much on suggested K dose by itself (since lots of the EI folks use KN03 and KH2P04 and I currently am not adding the N or P.

The dry ferts is not a bad idea. I'd know exactly how many mg I was adding...
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