Hi guys, just got my first setup from spiderfarmer, i’ve got Tropicana Cookies Auto on hydroponics. Unfortunately i have been having the issue you can see in the pic. The bottom leaves seem to be rusting which should be a ph problem, but the ph has been more or less stable (5.7 to 6.3 range). Looking for help, I flushed the solution a few days ago and replaced it with a new one but the problem persists.
Thanks in advance
https://imgur.com/a/x75FSsW.
Rusty spots on lower leaves in hydro can be from a few different issues. pH swings can lock out calcium and magnesium, which show up as rusting or spotting. Try to keep your reservoir steady around 5.8‑6.0 and avoid big swings; it’s worth calibrating your pH pen if you haven’t recently. Autos don’t need heavy feeding early on, so double check your EC/PPM and consider using a Cal‑Mag supplement if you’re using RO or filtered water. In hydro, high water temps and low dissolved oxygen can also stress roots and cause leaf issues – aim for water temps in the mid 60s°F with plenty of aeration. Keeping those parameters in range usually clears up rust spots within a week or two.
Hey! I know, I am a bit late here.
The rusting on your lower leaves could be a nutrient lockout or deficiency (iron, magnesium, or calcium) even if your pH looks stable. It can also be normal aging of lower leaves or stress from water temperature/oxygenation. Keep an eye on new growth if it looks healthy, it may not be a big issue; if it spreads, check nutrient balance and water conditions.
I had the same issue with my first hydro grow — rust spots on lower leaves even though pH looked fine. Turned out my EC was a bit too high and the plants were getting slight nutrient burn. After dialing back the nutes and keeping pH closer to 5.8 steady, new growth came in healthy. The old leaves didn’t recover, but the plant bounced back fine.
The comment about EC being slightly high rings true for me as a likely starting point — a flush resets the reservoir, but if you refilled to the same strength the lockout can return. If you’re seeing rust on lower leaves only while new growth looks clean, that often points to magnesium or calcium, especially with filtered water. I’d verify the pen with calibration solution before chasing nutrients, since a drifting reading can mimic stable pH. Also worth checking water temp and aeration, as mentioned earlier. What’s your current EC and res temp?
Agree that EC is the first thing to check here — flushing only resets the reservoir, and if you refilled to the same strength the lockout just comes back. If the rust is only on lower leaves while new growth stays clean, that leans toward calcium or magnesium, especially with filtered water. I’d also second calibrating the pH pen before chasing nutrients, since a drifting probe can look stable. What’s your EC and reservoir temp right now? That would tell you a lot before you change anything else.