Pretty sure its 100% caused by SeaChem Excel
I have the same problem. I bought two bunches and I was able to plant the entire front. It was gorgeaous. I use DIY C02, 2.5watts per gal, a Fert regimen, bi-weekly water changes. I know my tanks needs and have learned how to give it what it needs. My planted 30 is pristinely ran. I had contracted a stomach virus that kept me in bed for 6 days. I was un-able to do anything and the CO2 crapped out and for 3 days. a few things went haywire. most of all, a pretty impressive display of the tenacious BBA hair algae that I hate like no_one could truly ever comprehend!
I've dealt with this demon a few times and I know Exactly how to destroy it, then keep it away.
(THis is irrelavent to the excel problem, but read if you have bad BBA)
---MY BBA KILLING TREATMENT----------------------------------------
I usually pull out any NON planted infected plants, and any other parts that are covered that aren't directly rooted. I do a decent H2O2 Bath for 24 hours in a bucket with 3gal of treated water. Rinse heavy with clean plant friendly Water in 24 hours and put them back. Every spec of algae is dead, and the plants are fine.
Now for the planted ones... I use no more than 1-2ml per gal 3%H2O2 in a 3ml syringe, w/needle and turn off every thing that cause motion in the tank. then spend about 2 hours or less painstakingly dosing every piece I see. Your tank will quickly fill with micro O2 bubbles.. That means its working. after treatment, wait 30mins, or until the 02 reaction is over, and resume normal operation. In the morning. You'll notice all the algae is bright red. and pretty much dead.
--- END TREATMENT REG --------------------------------------------------
HOwever I was still too tired from that Virus, so I decided to try Using Excel to kill the BBA. MAny swear by it...... And about 2 weeks later after dosing every other day, It had unleashed an onslaught of melting on the DHG starting in the mid and working out, also hit my corkscrews vals, Italian Vals, and Dwarf Sag.
BUT.... THe Java ferns, the Cardinal plants, the ludwigia repens, and the amazon swords, all have quadrupled in growth and are displaying growth rates I never even thought possible!
Still the a fore mentioned are getting worse, even after I stopped Excel 6 days ago.
I knew there was a chance it'd hurt the vals, but didnt consider the Dwarf Hair Grass.
Anyway, Im going to let it go and see if it comes back, because i'm sure if you pull some of yours up, you'll notice the start or maybe even some nice new deep roots.
I'd bet on it man, Stop with the Excel. THis is what mine is looking like now: