Water temperature for Mozambique Tilapia
Tilapia are tropical fish and need warmer water temperatures. Depending on where you live this is more or less of an issue. My system is located in Southern California. I started my system around October. I live on the outskirts of the Mojave Desert and it can get quite cold at night. It does sometimes even drop down to 30F/-1C or so. I put my fish tank into the ground, which helps with keeping the temperature constant to some degree. I was so excited about getting my Tilapia in the beginning that I didn’t pay much attention to what water temperature I would have to maintain. Eventually I measured it and it was around 64F. This is kind of borderline for Mozambique Tilapia. I have about 45-50 fish in a 250gal tank. When I fed them, they were moving very slowly around and didn’t show much interest in the food. Well, maybe they were interested, but probably too stiff to swim. I didn’t want to risk losing fish, so I ordered two 300W aquarium heaters to bring up the temperature a bit. These heaters just plug into a standard wall outlet and have a built in thermostat. I cranked them up to maximum temperature. I also added a digital thermometer to check on the water temperature. I noticed that in the morning after a cold night, the temperature was getting barely above 67F. Ideally the water temperature should be between 80F to 85F. I didn’t want to significantly increase my electric bill and settled for 75F as my target temperature. The fish were still rather sluggish. I had seen Youtube videos of people feeding Tilapia and they would go crazy splashing and sloshing around everywhere. I had a hard time believing that 600W in heaters would only bring up the water temperature up by a few degrees. I calculated how much energy it would take to bring 250gal up to 75F from 63F and arrived at the required energy that was required. Ideally you would want your heating system to cycle – turn on and off, rather than being permanently on because it can’t make up for the temperature losses.
Here is the formula I used: Required Watts = [3.1 x Gallons x Delta Temp (F)]/# of hours to heat]
(3.1 x 250gal x (80F-60F))/12hrs = (775 x 12)/12hrs = 1291.666 Watt
My thought process for using the above numbers:
– Even though my target is 75F, my heating system should have some reserves built in. Hence I selected 80F.
– The above formula also doesn’t really take any losses into consideration. In other words, it assumes that there are no temperature losses while the heater is heating up the 250gal of water. This would only be true if the ambient temperature is the same as the water temperature, or if the ambient temperature is slightly higher. So the heater needs to work harder, since it needs to overcome any losses from the ambient on a cold day or night. This is also the reason why I chose 12hrs for the heating period. I could use 24hrs. The result would then tell me that I only needed 387.5 Watt. However, I already know that this is by no means sufficient, since I already had 600W heaters installed and they couldn’t keep up.
I didn’t want to calculate losses, since that would get too involved for a hobby.
Selecting Heaters
Based on my calculations above, I could just add two more 300W heaters and call it a day. However, while thinking through this issue, one of my aquarium heaters actually failed. Now there was an urgency to get things done. Something more robust was required. So, I actually designed my own water heating system. (I can’t help myself!).
I sourced a 1,500W water heater heating element from McMaster for $12 or so. I purchased a small and inexpensive PID Temperature controller and a solid state relay, since the controller’s relay wasn’t strong enough to switch the 1,500Watt heater on. I added another pond pump to constantly flow water across the heating element to avoid it burning up or melting my plumbing. A trip to Lowes provided me with the necessary plumbing supply.
Actual System Setup & Parts
Below are some photos from my current setup. It is not completed, yet. To save time I threw the temperature controller and solid state relay into a plastic box with a lid. Please do not try this at home, unless you are a trained electrician! This system operates on 110VAC. This voltage is life threatening! Especially when this is being operated in or close to water.