Aquaponic Gardening

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The water temp is a problem that hopefully will be resolved with a solar heating sys I am building. What is the optimal depth for a DWC? I used a hydroponic example for lettuce grown in a tank. I feed the fish based on the ammonia level, usually what they will eat in about 15 sec once a day. Some times I get a high nitrate reading. This could be do to the fish ratio?



Hi Jack,

The recommended DWC minimum depth is one foot, although you can go deeper if you wish but is not necessary to do so. Your fish ratios are almost double for your system so you can remove up to 50 % of them, or you can keep what you have and control the feeding to maintain good water readings. Getting a spike in the Nitrate reading before it levels off is not considered a problem whatsoever. When you control the temperatures, your entire system should become more efficient.

I appreciate your attention to my problem and the information you have provided. I will complete the solar heater and let you know how it is working. In the mean time I am going to use two 2500 watt  water heater elements to bring the temp up, "not the most economic way". Our morning temps have been in the twenties the last weeks and forecast is low for the next few weeks.

Again thank you very much.


Hi Jack,

Keep an eye on the nitrifying bacteria with those low temps and monitor regularly for ammonia. Get the temps stable and keep posting with updates. See this link

Harold, I've got a couple questions. 

Why is Jack's water temperature an issue? Lettuce love cooler temperatures. And as far as nitrifying bacteria, well, his nitrates are at 60-80ppm, which shows there is nitrification going on, and at an adequate rate for his plants.

Also, what is it about a 12 inch DWC bed that makes it better for plants than an 8 inch? In a media bed, the concern is the balance between the size of your biofilter and maintaining aerobic conditions. However, I'm curious what the appeal for the full 12 inch design is in a DWC besides stabilizing water temperatures because of the insulating effect of the extra water.

Jack, I'm wondering if your plants have a nutritional deficiency of some sort...

Nutritional deficiencies can be cause either by an actual lack of a nutrient available to a plant, or by something hindering the uptake of said nutrient. Sometimes your pH levels can lock out nutrients from getting to plants, other times the presence of other nutrients can "tie up" specific nutrients, which then rely on a healthy population of specific bacteria to make them available again.

Do you have any other plant systems besides stunted growth in your lettuce? Often, it can be something that one might ordinarily brush off as just "something that any plant does". Yellowing leaves, leaves that are darker than normal, purple spots (especially on peppers and cucumbers), things like that.

Also, wanted to ask you about your specific strain of lettuce. Are you meeting the requirements of whatever strain you are using? Some lettuce are less tolerant to cold, others are bred to love it. More sun, less sun, it can vary from strain to strain.

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