I have a low-tech five gallon Fluval Spec V with dwarf water lettuce, cryptocoryne undulata 'red', dwarf hair grass, an anubias nana 'petite', and a single betta. Initially, I was dosing API Leaf Zone, Excel, and nitrogen, and everything was fairly happy and growing, but I was also having cyanobacteria issues. When I ran out of Leaf Zone, I wanted to switch to something more comprehensive, so I got ThriveC
(I considered mixing my own, but given the size of my tank, I thought it was worth the convenience fee to get pre-mixed) and the GH booster
recommended to go along with it (my GH is super low to begin with anyway, so I figured it could only help).
I made no changes, other than stopping the Leaf Zone and Excel and starting ThriveC (1 pump 2x/week) and the GH booster. Almost immediately, I had an algae/cyanobacteria bloom, and I started noticing pin holes in my dwarf water lettuce leaves, starting on the oldest leaves. I initially thought it was likely due to an excess of nutrients that the plants weren't accustomed to, so I pulled back to the minimum recommended dose of 1 pump 1x/week.
Over time, the cyanobacteria died off and the tank is the most algae-free I've had it in a while...but my plants aren't growing. The dwarf water lettuce has pin holes and the old leaves rot off quickly, keeping them small and all their energy is going to maintenance, when before they were throwing babies left and right. The crypts took longer to develop holes in their leaves, but they eventually did, and I've not seen new babies in a while, when before I was pulling them out constantly. The dwarf hair grass isn't spreading. The anubias hasn't put on any new leaves.
So I figured 1 pump of ThriveC 1x/week wasn't enough, and I gradually worked up to 1 pump every other day (more than the recommended maximum). Still no algae/cyanobacteria, which is great, but no improvement to the dwarf water lettuce (if anything it looks worse - I'm seeing new holes on younger and younger leaves). I wouldn't expect to see a change in the other plants quite yet, based on how long it took for them to show problems, but given that the water lettuce hasn't improved, I'm not expecting them to either, and I'd rather fix this now than wait.
During this whole time, I've not made any changes to my lighting, the supplemental nitrogen dose, my weekly water changes, or anything else I can think of, so I'm quite sure it's the switch to ThriveC + GH booster that triggered it (not gonna lie, I'm pretty mad I spent extra money on the convenience of pre-mixed all-in-one, and it made everything so much worse...).
From what I was reading, holes in leaves can indicate a potassium deficiency, but I wanted to get an expert opinion before I went out and bought any new fertilizer. I've attached pictures showing the dwarf water lettuce and the crypts (the hair grass and anubias both look normal, just not growing). What do you think? Nutrient deficiency? Nutrient excess? Something else?