Greetings Bulletproof2:
The ppm requirement of cucumber is 1190-1750 and the suitable CF is 17-25, while ph is 5.5. The information is from the "Hydroponics Plant Guide" in Midwest Hydroponics. You can run a search on this or check the link below. out.
Ed

Here is a link that might be useful: Hydroponics Plant Guide

The midwest hydro link listed has EC for capsicum at 1260 ppm to 1540 ppm.

I have been growing chiles in aero/hydro for 10 years, keep accurate data and find the best range for capsicum between 450-550 ppm.

If you raise the EC, keep a daily log to see if the effect is beneficial. I think the kind of system you use influences EC levels.

It is equally possible that your EC is too high as well as too low.

Sorry for my ignorance. I am not familiar with cucumbers, but is Dasher II Cucumber the same as capsicum? The data in Midwest Hydro didn't specify Dasher II.

I think the point is if the information on capsicum is questionable, the rest of the information might be in question. If you look at some of the various sites that list EC information, they are all the same. Some sites have EC information, & some have PPM information, but if you convert them, you come up with the same values. Where the data comes from is unclear, which is why information from growers or cited sources may be more reliable.

High rates of evaporation or transpiration can raise the EC.

I raised the PPM to 640 and it killed it from overfertilization (4 week old plant), a person from general hydroponics told me to raise it to 1000, so I thought I should try 640 first and that was too much. Back to the drawing board.

Bulletproof2, here are some sites with material on hydro cucumber growing. They do not give an answer to your question other than what is said above, but they may be of interest to you.

Growing Hydroponic Cucumbers in a Plastic Trash Container

http://www2.ctahr.hawaii.edu/oc/freepubs/pdf/HG-44.pdf

Greenhouse Cucumbers
http://www.lpl.arizona.edu/~bcohen/cucumbers/greenhouse.html

KEYS TO SUCCESSFUL TOMATO AND CUCUMBER
PRODUCTION IN PERLITE MEDIA

http://www.schundler.com/keys.htm

I wonder if part of the problem might be that there is more than one ppm scale and how do you know which one is being quoted? One ppm scale is the EC X 700 and the other is the EC X 500. That could be a pretty drastic difference at 1000 ppm.
I'm growing some cuc seedlings and they are just putting out the first true leaves. I started them in a weak nutrient of about 4-6 CF. I have slowly brought it up so that now I'm around about 12 CF. This is around 600 to 840 ppm (depending on scale) and the seedlings still seem ok. Granted it has been raining a bit so they are getting some fresh water rinse as it is an outdoor system. I'm guessing that part of the trick is to adjust the levels slowly so the seedlings have time to adjust and if there is an adverse reaction you have time to react before killing the babies.

One thing I'm noticing about the cucumbers is that they are not the fastest off the mark. My squash and zucchini are so far ahead of the cucs even thought the seed packet give the same time to maturity for the cucs and zuccs I don't believe them at the moment.