I have bluelab PH and PPM pens, I wait till the numbers don't seem right before I calibrate. My nutrients usually take my water down to ~6.0 anyways (I still double check on res change outs, but not if I'm topping off a res) I have had to calibrate my ph pen once in the past year and even then it was only off by .1
Wanna hear a funny story about the ppm pen? Okay, trust me its good. So there I was I had just finished topping off 5 DWC buckets I had going. They were Black Russians about 4-5 weeks into flower Stuck my ppm pen in to make sure the nutes weren't too bad. I was staring at the little screen and watched the numbers go from 300 to 1000 to 3000 to 4000 to or. I don't know what the hell or is, but the second it went to or I flipped a shit and ran to my calibration solution. I was praying to the good lord in heaven something happened to the pen and the readings were way off. Stuck it in the calibration solution, and the reading was dead on. I rechecked the bucket, then checked all the buckets. Every bucket did the same thing. started off low, jumped up, jumped higher, stopped reading the numbers. I was panicking at that point wondering how in the holy hell I managed to get my ppms to such a grossly high level, without sticking the meter in a bottle of nutes. I had been following the feeding cart, estimated ppm from botanicare was ~2k I had tap water that started at 800 and I usually don't give them full strength so my ppms are around 2400 at this point normally. I stuck my plants on the rack I built. Its two pieces of wood with some space in between to hold the bucket lid with the net pot and allow the root ball to hang between it. I started dumping buckets and refilling them with water, but I was still curious at this point as to what the fuck happened so I didn't dump the last bucket just yet. I nuted the water in the 4 new buckets, busted out my meters and took some readings. 5.9-6.2 ph across the board, ppms 2370-2450 iiiiiinteresting. Rechecked the or bucket. Meter jumped to the or reading. This is where it gets super fucking peculiar. I took the smallest weakest looking plant I had. It recieved little to no light from the 1000w as the other plants overshadowed everything but its top cola. and stuck it in the or bucket. I like side by sides and experiments and I'm not adverse to sacrificing a plant here or there for science. I put the rest of the plants back into the buckets with proper readings, placed them under the light and let them grow. I monitored the OR bucket plant very closely, checking the leaves every 12 hours for signs of damage, deficiencies of any kind, most importantly for burn. Nothing. 5 days of having a bucket with 4000+ ppms and the plant showed nothing. No burn, no damage of any kind, it just kept on trucking like it had been. It was drinking water at the same rate as the other plants (Well a little slower, but thats to be expected as it was growing a little slower to begin with from lack of light). So, in conclusion, I have no idea what happened. I don't know what was going on with that bucket, or what was in it. Whatever it was it didn't harm my plant at all, and I still want to figure it out. Anyone ever experience anything like this?
Meter was set to 500ppm/tds measurement range is 0-5000 so it must've been over 5k