Hydros21 sensors not returning data

We are unable to get our Hydros 21 CTD sensor to return data. We are getting -9999 values on both the SD card and the website. All the connections are secure. The SDI-12 address is set as follows:
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<div>     const char*   hydrosSDI12address = “1”;  // The SDI-12 Address of the Hydros 21</div>
<div>     const uint8_t hydrosNumberReadings = 6;  // The number of readings to average</div>
<div>     const int8_t  SDI12Power = sensorPowerPin;  // Power pin (-1 if unconnected)</div>
<div>     const int8_t  SDI12Data  = 7;               // The SDI12 data pin</div>
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<div>We switched out the Hydros 21 CTD with an extra one we have and get the same results.</div>
<div>We have run out of ideas and are looking for any suggestions of things to try to resolve the issue.</div>
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