I've seen this with Java fern and a few other plants, they melt in response to CO2.
Having had chronic CO2 issues on a number of client's tanks over the years really tells you if things are going right, if they add the ferts 2-3x a week, and they say so, it's very likely that they did.
But that just leaves the CO2 and when the rate is dropped and they have a low sump water etc, or have reduced it up because they think the fish are having issues with the CO2, that's when I see lots of CO2 related issues.
Hygros, Java fern, Bolbitus in particular seem to do this.
I've had issues with CO2 - I killed all my fish (but one hardy Black Molly(!)) a couple of weeks ago with too high CO2, so the CO2-levels have been all over the place recently..
I've found it hard to eject as much CO2 as I want to get the plants pearling with really low light. It almost never pearl anymore since I've changed from a 310-litres high-tech with 0,7 watts/litre to 60-litres with 0,5 unreflected bad watts/litre.
(With "bad watts" I mean a couple of ordinary economy lamps (2x7 watts) and one 10000K Aquarelle 15 watts.)
Even when I had insane CO2-levels (with mist!) that killed my fish I had next to no pearling, so something is totally out of whack with my tank. Just can't figure out what it is. More PMDD doesn't help and not CO2 either it seems. All I can think of next is really bad light.. It's getting frustrating..
I dose this about 2-3 times a week:
2,5-5 ml KH2PO4 (2 tsp in 200 ml) which translates to 1,4 - 2,8 ppm.
0.2 tsp dry KNO3 which translates to 11 ppm NO3.
0.2 tsp dry Dolomite
5 ml micros (1,4 tsp in 500 mls of water + 1 tsp MgSO4 +2 tsp K2SO4) which gives me ~0.07 ppm Fe and some K+Mg.
That seems about right, but I wouldn't call that PMDD. PMDD is the now ancient formula for fertilizing that contained no phosphate and little nitrate. You are using the EI method, instead. When we buy fertilizers from Greg Watson, the bags have printed on them the old PMDD formula, so some people have thought that was what Greg recommends they should mix up for fertilizer.