macro's 1st DWC!- got a few questions

Hello, this is my first grow. Not just DWC but in general.
I've done a lot of research and got pretty far thanks to lurking around here a lot.

I'm not really sure if the results of this grow are going to turn out very good, this first time is just a learning experience really.

I'm growing these 6 clones that are from a cannabis club, they came in fairly crappy condition, looks like some kind of nute deficiency right off the bat. They're doing better than originally though.

Technical Details:
-Growing 6 sour diesel clones in a 18gal Sterilite res.
-Sensi-Grow 2 part nutes (800ppm)
-Tetra Whisper 60 Aquarium air pump
-2 10" Air Stones
-400wHPS light on 18/6 (400 MH is still in the mail, switching when it arrives)
-Ph is an "estimated" 5.5-5.9. I'm no good at reading chem drop ph tester, digital coming soon :)

I'm not really sure the age of the clones but they've been in my DWC for 3 days and I have a few questions:

Question 1: I'm not sure if this is algae or not but it's got me worried, in photo1 you will see on one of the air lines for the stones is a brown growth/substance on the outside of the line, also in the 4th uploaded pic is a brown substance visible on the wall of the res, those lines are from my finger investigating. On the res wall it didnt really feel like algae, like maybe the nutrients collected on the wall? is this likely? But on the air line it did feel slimy like algae..

In the 2nd pic you see I am using a blue top, I thought it was fairly opaque until I investigated as you can see in pic 5 a good amount of light seems to be getting through.

I've attached an opaque bag to the top, covering the blue, think the darkness is going to be enough to kill the algae and prevent future growths?

Should I drain it and scrub out the algae?

Question 2: The leaves in photo 3 are droopy and discolored, from investigation it seems like just a nute deficiency. Plants do seem to have some new growth absent of the discoloration and droopiness.. so they seem to be bouncing back. Just trying to get a 2nd opinion :)

heres a photo of the adjustment.
any suggestions so far?

i'll post photos as things develop

hi ya mate all seems ok, but jus a few pointers i have only jus started dwc and i am lovin it my plants are growing faster than i thought possibe the leaves are like solar panels, so fat dark green.... 1st the pump wisper dont sound good wots that 60/l an hr??? i have 2 oxipots with a 150/l hr standard in each with a 500l/hr pump split between both of them, so thats 800 litres an hr per 2 plants, all hoses need to be light tight, also i have seen people say use half power nuets but i have been using more and more and it jus grows faster and faster, maybe the more o2 ya put in the more nutes it can take but thats not a defo, cheers mate keep updating.

I'd start off getting a true ph meter and getting exact readings. You will need something better than drops for hydro.

Several thoughts....did you pre treat that hydroton? Do these plants have roots extending into the water? You said it was DWC; then said they were clones. They look extremely droopy which could either be from overnute, ph imbalance or perhaps they just aren't getting enough water. I don't have enough info about your system to say.
But I definitely see issues with your plants' health......unhappy ones.

good luck.

You'll also need to change out that plastic for something that will allow more air to your setup.....perhaps duct tape or paint although I wouldn't be painting anything with a plant in there.....but dump the plastic. It's not only blocking extra air to your roots its creating perfect conditions for mold and fungus problems.

Saw you had a good ph meter coming.....good work! That will help you out alot.

Watch those ferts and ph. 800 ppm seems a bit high for vegging plants.