Weak stems. Brown dyeing leaf tips.

you can't mix a sanitizing agent with something like "piranha" .. you've just killed the beneficial microbes with the h2o2. i don't see the damage you speak of so it's hard to give an opinion. on the surface it seems like you've made a lot of assumptions based on inductive reasoning. low P will cause some blueish hue in the leaves. if it advances, you will see dark blotches low on plant. algea growign on top is no big deal. more frequent irrigations is a potential problem, not 10-20% runoff (or even more if you ahve good drainage qualities). Soilless growers give 10-20% runoff every single irrigaiton with zero ramification, so don't attribute your problem to that unless you were dumping 10x more water than necessary through it. that would only drown roots temporarily.. too frequent irrigation invites microbial growth in rootzone because it remains too wet the entire time. you can water too little and cause this too -- the lowe areas of substrate may not get very moist, but the top will remain wet which isn't good. Looks liek coco.. so stick to 30% perlite and do make sur you have at least 10% runoff as that is not a problem. it is a proper irigation habit for coco. if you want to do frequent irrigations, plant size must match the pot size. you still have to wait for some minimum weight loss (water being used) before you can re-irrigate. if the pot is too large, you have to wait. if the plant drinks enough fast enough relative to water capacity of pot (25%? 33% water-weight loss?), then you can re-irrigate. it's not just as simple as more frequently dumping water on it.. the contexxt must jive for that sort of technique. i'd get some runs in with zero problems with a normal, meat and potatoes methods then try somethign more sophisticated when you have a good baseline to compare and see whether all the extra hubbabaloo is worth it -- from what i read 2-3 irrigations per day will match any "hydro" method's growth rate. diminishing returns after that. even so, i'd recommend a good wet/dry cycle early on. seedlings and smaller plants wont drink fast enough, too often, to justify frequent irrigations, and there is benefit to stressing the roots slightly early on... they will be more robust and deeper if you follow the basics -- water entire thing until 10% runoff or more... wait for top layer to dry (pot will feel light) and repeat. by allowing top layer to dry out, roots will drive downward instead of growing more superficial roots... when you get near flip or enough vege time as passed, frequent irrigations can be more effective with a robust rootzone. roots form differently under different conditions.. very wet will have fewer fine hairs. dryer will form a more fibrous mass of roots with greater absorption capabilities. as long as there's enough "dryback" (poorly chosen term by whomever out there. it's not drying off, lol) you can re-irrigate relatively safely. you may get algea if light hits teh soil. if the canopy is full this won't happen as easily. algea doesn't harm plant... is superficial and is not much of a concern.