Bottom line up front: Manganese bottomed out, and I probably have more K than is necessary.
About 18 months ago I started the thread, Too Much of Some Fert? https://www.plantedtank.net/forums/1...some-fert.html
I was noticing much slower growth than normal across nearly 20 species in a 155-gallon tank with BDBS substrate, about 6-8 months after switching from very low CSM-B/DPTA dosing to a custom micro mix. Naturally, the first thing to check is CO2, flow and light, but I had done that multiple times. I got a 1.0 pH drop or more in area farthest away from the filter output, improved flow and O2 compared to earlier years where I got much better growth, kept lighting moderate (except a few times where I would blast the BML strip to try to induce some growth). I didn’t have problems with BBA or tip stunting, and virtually no algae problems at all. Had a little BGA emerge in spots, but it wouldn’t spread much and it went away. Root growth was all white and looked fine. Yet, little to no growth in most plants. Pearling was usually observed. Dosing was ½ to full EI on macros, and most often ¼ to ½ EI on Fe/custom trace mix, using various Burr formulas. I had issues in the past with CSM-B like Burr, and since AR was an affected plant here, I wanted to be careful on micros. I also had some O+ in the substrate. I changed 50-70% water weekly.
Persicaria Sao Paulo
Lymnophila Belem (some growth, but all green)
Ammania Senegalensis (got rid of it eventually)
Pogo Erectus (got rid of it eventually)
AR Mini and Regular
Anubias, Buce, Java Fern, Broadleaf Sagittaria and Crypts (for the most part) didn’t have issues.
Things that didn’t help at all:
1. Putting AR and Ammania Senegalensis in pots of garden soil and generous O+. Nothing happened at all to either plant.
2. Floating plants at the surface
3. Full O+ and Osmocote N/P/K in substrate under affected plants. Didn’t notice any difference.
What partially worked – cleaning the whole tank, uproot and vacuum everything. Clean filters. This helped L Rugosa immediately, and I saw some very slow growth in Acmella Repens emerge, but not as fast as before.
Fast forward to a couple months ago, and I really focused on what plants were telling me. Hygro was full of pinholes with a lot of leaf shedding. Slow growth and deteriorating old leaves on stems (partly due to never needing to top them off) pointed to K and mobile nutrients, so I would add 10-15 ppm K at water change, plus the K from KNO3. I added some extra Zn to eliminate that as a limited mobile trace element. Hygro got worse, and shed everything but the top 1-2 nodes. Never seen it look so bad, and I was sure there was adequate K. AR mini and regular were not stunted but also not growing at all. Leaf tips would curl down in several species, so I got a Ca test and normally measured between 30-40 ppm.
I decided to follow Surf’s advice and get the water tested by ICP Analysis. I sent a tank sample, which had two macro and two micro doses since the last water change. This would give me an idea of what was in the tank, and hopefully point to a smoking gun, so to speak. Here are the results, all in ppm:
Ca – 29.2
Mg – 15.06
K – 40.53
P – 2.29
Fe – 0.061
Mn – 0.00 (this was the biggest shock-I always had 1:3 to 1:5 ratio with Fe in the mix)
Zn – 0.086
B – 0.14
Mo – 0.012
Cu – 0.012
Ni – 0.007
Na – 6.56
Cl – 8.38
S – 38.4
Conclusions: Tap probably has some Zn, B and Cu that isn’t showing in the local water report. My scale might not be accurate in the 20-50 mg range, and that range is what I measure Cu, Mo and Ni for the trace mix. Would probably be better to make a solution of those with hundreds of mg in it, and then use a portion for the trace mix. Could Mn deficiency be the smoking gun here? Easy enough to add some and see… The test also shows I have more K than needed, and I could increase PO4 some more. ICP-Analysis doesn’t measure NO3, but I have the Salifert kit for that. Based on these lab numbers, I probably have 10-15 ppm NO3 based on my ratio of dosing with PO4. Salifert reads higher than that normally – for me it would show 15-25 ppm. Since Mn and Fe assist with K uptake, perhaps a relative shortage of those are contributing to the hygro pinholes and leaf shedding. Anyway, I’m very glad I got the test. I never would have guessed that Mn would be zero! I wonder how I'm getting growth in anything if Mn is zero, though.