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Front loading macros - a few questions


Community Member
Jul 20, 2023
My 100 gallon tank was cooking along just fine until a few months ago when my large Amazon Sword started struggling. Yellowing of leaves. Just not as robust as normal. Other plants seemed to be ok. It's a low tech tank and I do roughly 20% water changes weekly. I was dosing PPS-Pro with daily micro and macro doses per the recipes on GLA's website. I then read about front loading macros and got Greggz to help me get started.

I have a 32 gallon Brute can with roughly 29 gallons of water in it. Targets are NO3 -25, PO4 - 2.5, and K - 32. Using the Rotala Butterfly calculator I came up with a formula that adds KNO3 4.47g, KH2PO4 393mg, and K2SO4 245mg. After starting that routine, the sword began to look better but after a few weeks started to go downhill again.

Then I read Joe's advice against front loading with such small water changes without adding in additional doses of macros during the week. So when I was mixing up last week's water, I decided to test the Nitrate (in the makeup water) prior to the water change. Using the Salifert test kit, I got a reading of around 10ppm. I tested again and got the same results. I added an additional 5g NO3 to the reservoir and retested and got closer to 20ppm.

So are my calculations wrong and I'm not adding enough NO3 to the reservoir? Or could the test kit be wrong? Or something else?

Is the sword your only plant your seeing major issues with? If that’s the case, adding a root tab underneath it would make a big difference. Echinodorus species are nutrient hogs so it would be one of the first to show issue if something is even slightly off.
Any ideas on the discrepancy between what I think I’m adding to the reservoir and what the test results say?