Certainly looks like a toxicity to me. Based on the given info, about the only deficiency it could be is CO2. LRJ has a good point, it is definitely too crowded. Plants compete for co2 just like nutrients. Give some room between plant groups and make sure the area gets adequate flow.
Also looks like it's due for a good trim. AR needs aggressive pruning. It is a tough plant, you can be merciless with it and it will come right back. I'd pinch all those bad leaves off, whole tops, whatever, all of it. None of that damage is going to correct itself, only new growth will tell the tale.
Maybe even uproot and separate the good plants from the bad ones. Probably some baby sprouts underneath all that still in good shape. Toss all the bad and replant the good ones, spreading them out a little.
Regarding toxicity, you are dosing micros at .1 ppm Fe...approximately? That is perfectly favorable for lots of folks, but it would definitely be too much for my tanks. Dont ask me why.
If the Ludwigia perked up when you reduced micros, that for me would be a concrete sign I was dosing too much. What I would do is a couple back to back 70-80% water changes, two days in a row with no dosing, then skip a couple doses of micros, then start back around 1/4-1/3 or so previous levels.
You'll know right away if its a toxicity because there'll be an immediate positive response after just a few days. If nothing happens after a week, or things get worse, then you can rule toxicity out and move on to something else.
Another thing, are you measuring out the csmb in 1/16 tsp doses? Be better to mix up a solution something like 500ml/5ml doses. Because csmb is comprised of several different things, and the chances of getting everything in the right proportion using such small amounts is slim. It is really made for hydroponics to treat 100s or 1000s of gallons at a time.
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Last edited by burr740; 06-26-2016 at 05:40 AM.