Help needed – heavy condensation in my Camponotus nicobarensis test tube and temperature issues

[u/DomeTosky]

Hi everyone! I’m looking for advice from more experienced ant keepers because I’m worried about my young colony.
I have a Camponotus nicobarensis queen with a few workers and some brood (larvae and pupae). They are currently living in a test tube with a water reservoir and cotton, kept inside a dark cardboard box.
My main concerns are condensation and temperature.
Condensation:
Over the last few days, condensation inside the test tube has increased significantly. There are now fairly large droplets on the ceiling of the tube, mainly above the queen and brood. One droplet has run down the inner wall to about halfway down the tube, but as far as I can tell, it hasn’t reached the floor or formed a pool near the ants.
The queen is often curled up in a crescent shape over the brood. I saw her moving yesterday, but when I briefly checked today, she appeared motionless in that same position. I don’t want to keep disturbing them to check.
Temperature:
My room gets quite cold. The temperature near the colony has been around 19°C, and it may drop to approximately 15°C overnight.
I bought a 7 W reptile heat mat (15 × 28 cm) with an analog thermostat. The thermostat is set to 26°C, but my old analog thermometer still reads around 19°C. I’ve tried repositioning the thermostat probe, but I’m not sure whether the readings are accurate. The thermometer’s sensor on the back may not be making proper contact with the glass.
For now, I’ve moved the test tube back into its original dark box, away from the heat mat. I’m planning to set up a secure outworld and eventually provide a gentle temperature gradient, heating only one end of the test tube.
My questions:
Can this amount of condensation disappear on its own, or is it a sign that the test tube could flood?
At what point should I intervene rather than leave the colony undisturbed?
Is approximately 15°C overnight dangerous for a young C. nicobarensis colony?
What is the best way to measure the actual temperature near the test tube and safely set up a heat mat?
Would it be sensible to connect the test tube to a secure outworld once it’s ready, or should I keep the colony in the tube for now?
I’d really appreciate any advice, especially from people who have kept Camponotus nicobarensis founding colonies. I don’t want to stress the queen unnecessarily, but I also don’t want to ignore a potentially serious problem.
Thanks in advance!

[u/Gelo_Man]

15°C is definitely too cold for a tropical species like nicobarensis, especially for a young colony. I'd aim for a stable 24–27°C. Condensation isn't necessarily dangerous unless water starts pooling or reaching the brood. Temperature fluctuations are likely contributing to it. If you're using a heat mat, only heat one end of the tube and use a digital thermometer to monitor it. I'd keep them in the test tube for now and avoid unnecessary disturbances.

[u/CeilingTowel]

Without going too technical, condensation occurs when temperature-drops happen too quickly.

The water and air in your tube are warm, then when the saturated air touches the cold test tube, the temperature plunges and the air sheds excess water vapour at dew point temperature.

Cut the long story short, your room temperature is way too cold, compared to the tube. The contrast is the key.

Try putting the tube in a unexposed box along with the heat mat(not the current one with two handle-holes and open top). The ambient air immediately around the tube must not be too cold. The box air will act as temperature buffer.

The condensation water probably isn't going anywhere unless you're able to bring the tube to a warm location where evaporation rate is increased. Currently, like you said, it has only formed on the ceiling, which makes sense since only the top of the tube is exposed to cold room air.

Connecting the tube to outworld will not change anything. The air around the tube must be at most <~2~3°C lower than the tube.

If you're able to find a cover-able box that fits the entire heat mat inside, your issue is completely solved.