dehumidifier Oversized?

over-sized wouldn't be a problem. Most work in a 5% range, and then you have the error of their hygrometer to consider too. As well as the +/- error % of your probes measuing atmosphere in garden. there's another potential 3-5% offset. Looks like 48% - 58%? You'd have to check your dehum's manual to see exactly how it works.. does it click on at the % you set then draw down a few percent below, or does RH have to go 3-5% above your setting before it clicks on and draws it down to your setting? Or, just observe it for a few minutes and see what the reading says when it turns off and on. If my dehum is outside the tent, there's also a fairly consistent offset that results. I know to set my dehum 5% lower than my target inside the tent. there's nothing you can do beyond centering how the dehum works with what you want. If it's a resulting 10% range, that's how that particular equipment controls RH. I'd expect most to have similar circuitry and work in a similar fashion, though that will likely vary by continent/region. Also, unless that temp is taken with an infrared thermometer pointed at bottom of a leaf, it's not an accurate calculation of VPD. It'll be 3-5F cooler at stomatas and RH will be higher within canopy even with good circulation. So, don't worry too much about a high VPD if the plants are growing well.. in fact you will need to do a little trial and error to figure out if a high or lower vpd is beneficial or not... if not using clones and a large enough number, then clones of multiple other genetics... can't be too confident with what you see.. So, just manage it as best you can :P From what i've read you want a .4 or less variance between day and night vpd, so .. already got that locked in. I bet your vpd if you calculate it withe a bit lower temps and a bit higher RH (depending on where your probe is), it's in a fairly healthy range. You can mitigate the effect on fertilization from too high of a vpd by dropping concentration of fertilizer slightly... and vice versa.