I have this spare tank which has been a plant farm, then an experimentation tank, then a quarantine, and now is a little of all of those at the same time. In practice, right now it is a tank with very old aquasoil, plants that are well established, but never in the best of conditions, lots of relentless green thread algae, yeast CO2, fertilized in the same way as my main tank with home mixed macros and commercial micros + iron.
The thing is that in this particular tank, the frogbits always die, and always the same way. I add healthy looking plants from the other tanks, and from the moment they touch this tank's water, all new leaves grow filled with holes. Old leaves remain unaffected. Other floating plants look OK...
Now, I can hear @dw1305 's voice in my head, obviously fictitious, saying that it must be an immobile nutrient, most likely iron. And because of this, I have been very careful to add iron to this tank in a rigid schedule for at least 2 months now. I also had a week when I added extra calcium and another when I added extra potassium, with no changes at all.
The tank's water is very soft, KH measured between 0.5 and 1.0ppm, water is mildly acidic. I dose the bottle's recommended dose for micros and add an extra 0.1ppm of Fe divided in three weekly doses. I don't know for sure what kind of Fe it is, but it is probably gluconate. Even though the plants in the tank aren't all that well, I don't see any clear signs of deficiencies like chlorosis.
At some point I discovered that the expiration date on my iron bottle was over an year past, so I happily bought a new bottle, from a different brand, and thought that was it, but unfortunately it didn't change anything.
In this picture, a recently added frogbit that has grown its first leaf in this tank, and one that has been there for a long time...
The thing is that in this particular tank, the frogbits always die, and always the same way. I add healthy looking plants from the other tanks, and from the moment they touch this tank's water, all new leaves grow filled with holes. Old leaves remain unaffected. Other floating plants look OK...
Now, I can hear @dw1305 's voice in my head, obviously fictitious, saying that it must be an immobile nutrient, most likely iron. And because of this, I have been very careful to add iron to this tank in a rigid schedule for at least 2 months now. I also had a week when I added extra calcium and another when I added extra potassium, with no changes at all.
The tank's water is very soft, KH measured between 0.5 and 1.0ppm, water is mildly acidic. I dose the bottle's recommended dose for micros and add an extra 0.1ppm of Fe divided in three weekly doses. I don't know for sure what kind of Fe it is, but it is probably gluconate. Even though the plants in the tank aren't all that well, I don't see any clear signs of deficiencies like chlorosis.
At some point I discovered that the expiration date on my iron bottle was over an year past, so I happily bought a new bottle, from a different brand, and thought that was it, but unfortunately it didn't change anything.
In this picture, a recently added frogbit that has grown its first leaf in this tank, and one that has been there for a long time...