All top leaves going yellow ???

Chrisjames47 said:

Thanks for the reply, I had the blue lab ph meter and it had some water damage so the digits on the screen went wierd but I would dry it out with a hairdryer before every use and it seemed to work but it ended up

Cheers, do you think passive with just the 4" is enough for now?

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I would personally get a new ph pen to be sure, I know they are not cheap but high or low ph will have a bad effect. It's also a good idea to calibrate it once a month or so. Alternatively, if you are using cana A-B, they do have a coco variant that is auto ph (you need to use it with coco ofc). Liquid feeds are not the cheapest way in the long run but would be a good option while you get everything else in order, such as out-take issues.

With a 6" out-take you can use an 8" small length of ducting for the passive in-take, it should be ok and will stop light leaching while also keeping smell down a little. You can use multiple passive intakes, even opening tent vents, it will put less stress on the out-take and is a better option if smell or light leaching isn't an issue. In the winter it's better to go with the 8" passive in-take to stop heat escaping so easily.

Bare in mind I do not know what country you live in. If it's a hot one, you may need an 8" out-take for heat waves, or consider cool tubes during those waves. You'd have to put that question to somebody in a similar climate if so.