Dark blotches in the center: toxicity or deficiency

Setup is rdwc
PH is 5.9 and steady
Room temp 72
Res temp 68-70
Ppm 150 of botanicare base and grow for 26 gallons of R/O

Seedlings are about a week old, started noticing some dark blotches along the center of the leaf today. Can't determine if this is a phosphorus toxicity or a deficiency. Any help is appreciated.

Thanks

A room temp of 78 would be much better. Show a root pic. Are there enough roots developed that the roots in the water are the plants primary nutrient suckers. First guess without seeing the roots would be deficiency due to low ppm. The leaves look like they are beginning to pale. There is no twisting or curling. 150ppm isn't much to eat even for a seedling no matter which conversion rate your meter is(might list that as well).

Phosphorus...

I assumed P deficiency, thank you the quick responses.

Post what you do to fix the issue and take a p8cture once you get things straightened out. If everyone did that itd be quite beneficial! Peace

I added some base and grow nutrients, bumped the ppms up to 480. I will post pics in a few days if things stabilize so everyone can reference it.

thanks again

Plants started to grow, but stalled and now the top leaves are browning. I'll have to flush and start fresh.