Make sure your res is light proof! The only way algae will grow in a res is if its getter light!

also, the number 1 reason why beginners have such a hard time controlling pH is because they dont rinse and soak there grow rocks or rockwool enough (you should also soak your air stones in a pH'd solution!). about a week before i start a grow using hydrotron or rockwool i will start soaking my equipment. At first i just wash my stones for ALONG time (if you notice there is ALOT of dust and residue on those stones!) then i let them sit in pH'd water for a few hours, then i come back and test the pH of the stone/water solution, if its changed i strain the water out and start over again until the pH doesn't change at all! then you have properly pH'd and washed stones. (same process can be used for rockwool)

Also, durring res changes you should SCRUB your res out (and i mean SCRUB!) you want to get rid of any built up salts that may accumulate on the inside of your res.

When it comes to oxygen in DWC you rly cant get enough, it is NOT POSSIBLE to overload your plants with oxygen! ...the more oxygen you can provide the better! Also another thing ppl dont rly understand about DWC is you want SMALL air bubbles (TONS AND TONS of small air bubbles) i use Micro-Pore oxygen diffuser's they are a bit expensive to buy but they will not clog or break down like cheap walmart air stones. i also use a GH dual Diaphram Air Pump (Which has 4 outlets, i use 2 outlets per 5 gallon DWC setup with to micro-pore diffusers in each res. You want there to be a froth of bubbles on the top of your res...

1. Is the slimy growth (whether bacterial or algae) something that should really concern me considering the frequency I change my res water?
-Yes, it should concern you, it means light is getting into your res, and could eventually lead to root rot and the death of your plants (Work on it!) id look into products like Hygrozyme or hydrogaurd (flourasheild is another one i think) and start using that and stop using H2O2
2. My leaves are very 'wrinkly.' Upon reading this forum, I concluded this is due to pH fluctuations (please correct me if i'm wrong). Is there anything I can do to buffer out the pH from fluctuating so much other than keep temps stable?
- your kinda along for the ride now, you could try and get some properly washed and pH'd hydrotron and change out as many of the pebbles as you can without disrupting the root zone but u arnt going to be able to get them all, hopefully your res will wash all of your hydrotron soon and your pH will stop fluctuating
3. My leaves are fairly droopy, which I've read is due to a too small of a air:water ratio in the rez.(again, please correct me if I'm wrong). How can I fix this considering I already have 2 airstones pumping a massive amount of air through this system?
-like i said, you can not physically have enough oxygen in that res, go out and purchase a bigger air pump and some better air stones, your plants will love you!