I don't grow in soil anymore, so take this with a grain of salt.
But I think she might be under-watered. Like Suki says, it certainly looks pretty dry. I did used to grow in
HF, and found it suitable for seedlings -- seems less hot than
OF.
My strategy in Happy Frog was to water every 2-3 days, working my way up to 500mL or so by the second week. This was in 3 gallon pots. This might seem like a lot, but that perlite really helps the roots stay oxygenated. A lot of the tutorials online really stress avoiding overwatering, but it's definitely easy to over-correct and underwater. Usually by 3 weeks in, I'd be watering perhaps a litre at a time. I don't think soil, or any medium, should be allowed to "totally" dry out, which is contrary to a lot of what’s thrown around.
Also, 6.0-6.4 is a little iffy. 6.5 is a safer target if you're able to raise the pH of your water a bit. It's a safe number too because if you don't have a fancy accurate pH pen, you get a bit of error margin on either side. Unless you're reading 6.0 on a BlueLab or something similar, it's very possible that reading is high and you're water is more acidic than you think.
Also, how's your light intensity? One of my first mistakes early on was blasting seedlings with too intense light. I find with seedlings, less light is better, as long as they’re not stretching too much.
Finally, FWIW, I started supplementing liquid nutes around day 15-20 in
HF. Granted my plants were usually a little further along. If you have been underwatering, there might still be some nutes in the medium, so Im apprehensive to say you need to start feeding right away. Maybe try watering a little more and see how she reponds, but be prepared to start supplementing nutes asap. When it comes to nutrients, check out Man O Green's "A Word on Nutrients" tutorial on the forum. It's a must read!
Good luck
