No EC meter... How strong should i mix nutrients and how often do i change it?

Just as title says lol.

It depends what stage is your plant in

Early stages of veg... like maybe 6 weeks old from clones.

i would start at a 1/4 then work your way up,2 be safe

I too don't use PH or PPM meters I can tell you what works for me. I use 5 gal buckets filled to with in 1-2" of net pot. I use GH Flora nutes. for veg I use 3 teaspoons grow, 2 teaspoons micro, 1 teaspoon bloom for flower I use 1teaspoon grow, 2 teaspoons micro, 3 teaspoons bloom. (That's teaspoons per gal.)Use the best water you can get. Try to avoid tap water if you can. I use rain water or spring water from a nearby spring. I fill for the first time with full strength nutes and top off every day alternating plain water one day and nutes the next. this seems to keep things in the ball park. I have had some great success with this simple feeding plan. Hope this helps

i also dont use a ppm meter, i use 1/7th of rec when i get a nice set of roots in bucket, then everytime i change res i add another 1/7th so by the time im in week 4 shes on half strength, jus make sure the bucket gets a gd rinse during res change. samee in flower, but i never take it over half. they always grow lush and fat,, my last grow give me 4 1/4 oz off auto ak

i use GH flora series as well and to tbh ive been using the full recommended dosage and sometimes more and have not seen any problems and 3 weeks from seed they are looking perfectly ok except they got stunted for some time due to root rot issues during the first two weeks which were solved with some gold old scrubbing and DM Zone. Just recently i found out about Lucas Formula though and I think at the next res change i will start using that formula. Its (Grow-Micro-Bloom/ ml) 0-5-10 for veg or 0-8-16 for flower i believe. it bypasses the use of Grow altogether. apparently you dont need it at all. just remember the formula is basically a 2:1 ratio of bloom and micro, with bloom twice as much as micro. For some time I was winging it with some Ph strips, and then for a week I had no way tto test the Ph, but luckily once i did get my Ph meter like yesterday i tested my res water and it had not passed 6.1. I never have used a ppm meter although next grow i might if this grow goes anywhere near as planned. i think its good to use your plants natural ppm meter, a.k.a. its leaves and the speed of growth. you'll learn a lot about your plants. Try lucas formula in smaller doses, and try to keep an extra jug of the nutrients so you can top off the res everyday or whenever its necessary. I notice my plants drink up a good amount mostly during the night and into morning, so i top it off when i wake up with a solution that has higher concentrations of nutes. for example lets say i had that 0-8-16 in a 1 gallon res, i would have another 1 gallon res with 150% the concentration so it would be like 0-12-24. idk if that is a good idea but to me i think its good to keep the "topping solution" at a higher concentration so as to make up for any deficiencies in nutes as well progressively exposing the roots to higher doses of nutes.

I use one, so I don't really know how to grow without it. After I transplant if I've added too much compost sometimes my pH will dive severely (new at this). If I didn't have a pH pen I'd be screwed, so I'd say just buy one.
Oakton's PCS Testr35 is temperature, pH, conductivity (ec), TDS, and salinity in one waterproof meter, horray!

Herbalife, I have the same pen for 8 months absolutely love the thing.

I use my ppm/ph meter sevral times a day and find that I only use it when mixing nuts and on a daily basis to keep everything in check that i can but I have city water that has a ph of 7.1 and 300ppm so lets say you need a mix thats about 900ppm I have to adjust a smidge since the water is already high. so I guess knowing what your waters ph and ppm from the tap (or wherever your water comes from) and then look around at your suppliers site for a faq page. Sorry I can only tell ya so much but I am only in my 4 round of regular ladies and my first auto. good luck and have fun REd Ohh ya fyi I veg at 920 ppm to 950ppm yet again it will depend on the maker (GH, cogo ect)