I have been using this for a year and a half. Works great. Figure a .5 multiplier to get your EC.
http://www.amazon.com/gp/product/B002C0A7ZY/ref=s9_psimh_gw_p60_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=0YM29JQ45C6RMNF9E7G9&pf_rd_t=101&pf_rd_p=1389517282&pf_rd_i=507846