questions about promix

[bower]

I'm using promix to start my seeds this year for the first time, because the local product I prefer was not available. I got a bag of the kind of promix that has no fertilizers in it, and so far it has worked fine for germinating my seeds on the heat mat (no damping off or other molds from the mix). I've now used the same stuff to pot the seedlings up into cell pack until they get some true leaves, using a pinch of bone meal as ferts below the surface, as I usually do... so far so good.

I was advised by someone who used promix often, that I should water from the bottom only, to prevent algae from growing on top. She explained that the liquid ferts (eg fish emulsion) tend to sit on the top, and this promotes the algae to grow.

Watering from the bottom would be a significant departure from my usual practice, and I have concerns about overwatering or leaving the plants with wet feet, especially my tomatoes which will be in a cool area. I usually give them as little water as possible, and have been really surprised just how little water they consume in those circumstances. I've always watered from the top, and never had any algae on the soil of the young plants, although my usual starting mix contains some compost. But the other difference is, I don't use liquid ferts on my seedlings. I just use a little bone meal, well below the surface.

Just to complicate my anxiety about this, I spotted and killed a small fly this morning that had landed on the edge of my heat mat/seed starting tray dome. I've had fungus gnat problems with in house peppers usually later in the season, and I know that improper drainage is exactly the condition they desire.

So, please give me your advice. Should I go ahead and water from the top as usual, as little as possible?
If not, what would you do to ensure that bottom watered seedlings are well drained? Please bear in mind, advanced technical solutions are not going to happen... it has to be simple and low tech in the circumstances.

Third question, as I understand the promix contains no nutrients at all, so (if I use bone meal as usual) they won't be getting any potassium which would normally be available via the compost in the mix. Maybe I should get some compost to add for the potting up stage? , if I still can't get my preferred stuff and have to stick with the promix (at 4 X the price I might add ).. If you use promix for potting up, how do you fertilize? (I don't use chems, so what is not organic will doubtless fall on deaf ears).

TIA for your help!

[JamesL]

Bower,
Algae - Would agree that fish or seaweed will cause it. It doesn't bother me (or the plants) at all. If it crusts you can always poke holes in it.

[bower]

hi James,

I get algae in my greenhouse tubs on at least a seasonal basis.. I find it super smelly and spreads really fast (smell is probably moist air loaded with spores!). I take it as a sign that the pH is dropped, so I remove the 'crusty' layer and give it some lime, then it doesn't return - and my plants don't get calcium deficient or any other ills of low pH.

It makes sense that fish watering (mainly N) would lower the pH and make the algae grow.

My well water is actually alkaline (due to manganese, not calcium, unfortunately)... so a little top watering should not encourage the algae, I think.

ps. love your soil blocks... they look like little frosted brownies!