slow plant growth rate

[Kevin R.]

Hello all!

 

Can anyone tell me why I would be having a slow growth rate with my plants in my system? The first setup I have is lettuce/ basil growing in a raft setup in a 40 gallon tank with a 4" bluegill. The plants get direct indoor light from 2 t5 bulbs about 2' away from plants for 12-14 hours a day. The second setup is same plants in an outdoor 235 gallon tank with approx 50 1-2 inch comet fish and 25 or so minnows. This is set up as flood and drain into 2 55 gallon half barrels with hydroton.

 

both systems seem to grow at a slow speed, in fact I have plants growing in a dirt planter in a window sill that are bigger and growing faster than both aquaponic systems.

 

I dont know if this is enough info to remedy my problem or still to vague, but I have always read that aquaponic systems grow way faster than normal growing methods.

 

Any ideas/tips Folks?

 

[Robert Pugh]

I have a very tiny set up outdoors, so it is very different from your systems, but I also have slow growth. 

Increasing the flood/drain cycle time took it from 0 growth to slow growth. The roots needed more time to dry out in between cycles.

I figure nutrients are another thing to consider. Nitrate levels have been high, 160ppm, so no lack of nitrogen. In fact, what does grow is nice and green. Not sure what else I can measure, but I would be interested in the comments of others on this point.

I'm suspicious of my pH, currently at 8.0 on a well cycled system. I wonder if this is interfering with nutrient uptake.

Maybe sharing your water chemistry is a start:

- pH

-Nitrates

-Nitrites

-Ammonia

[Jon Parr]

Robert, pH is way too high for your plants, and your nutrient uptake is most certainly impaired. Lower it and you'll be amazed. I prefer HCl (muriatic acid), and lower slowly. To estimate how much acid to add, remove a measured portion of water and experiment with a little acid and monitor it's effect, then calculate a dose for the whole system based on your findings. Common advice here on this forum is to not change pH more that .2 points per day. That's probably great advice, but it would take forever to lower hard water starting over 8.0, who has time for that? I personally haven't had a problem with an immediate fluctuation of 1 or 2 points lower after just a few minutes of circulation. Ive even done some foolish doses that lowered pH from 8 to 4 in five minutes. Crazy! And my pangasius catfish were freaking out, running into glass, burrowing into gravel, jumping out of the water. The tilapia and redclaws in the same tank were completely unaffected, just business as usual. Even so, the pangasius recovered and no fatalities. The next day the pH had rebounded to 7.9, and this is a normal and expected phenomenon. The acid needs time to balance the bases, and an immediate reading will not be accurate. Anyway, test your pH, record, add a little acid, after a few minutes of circulation test again to make sure you didn't overdo it, then ignore. Test again the next day at the same time (daily CO2 cycles will cause the pH to swing daily about .2-.4 points or more, lower in the morning, higher in the evening, so test and record at the same general time each day). Likely the pH will have returned to previous day's level, or slightly lower. Record, add a little more acid, ignore. Repeat this process daily. At some point it will start to drop. As it does, the same dose of acid will have more and more affect on pH, so be careful not to overdo it as you near your target pH. Once it gets there and holds for a couple of days, you are golden. Your plants will thank you with an explosion of growth. In a healthy, aerobic system, the pH will drop a little every day. That's a fact. That is why some folks need to add a base like KOH or a carbonate like oyster shells in order to counter-act the acidifying affect of nitrification. Why, you ask, is your system still 8.0 after being "well seasoned"? Good question, I'm glad you asked. Because the nitrification process is mildly acidifying compared to the base components of hard water, and regular top-up water adds more base to the slow battle that the bacteria are fighting. Once the bases are neutralized with your HCl acid, then the nitrifying bacteria can begin to win the battle. Depending on your particular water chemistry, you may have to add something to your system to keep the balance. So far for my big system, less than 2 months old now, the pH will drop to about 6.0 before needing to be topped up. My well water is currently 8.8, and this hard water is all that is needed to buffer the water back up (actually I still need a little acid if transpiration is high, meaning more hard water per unit time). It originally took about 2 gallons of 14.8% HCL to bring 2200 gallons of total system water down from high 8's to high 6's over about a week's time, and maybe a quart since then to fine tune. To make this all more confusing, my well water will soften as the rains fall, to about 7.0 by spring, then harden up again as the dry season ensues. So, I will have to adjust my regimen as the seasons change. 

Kevin, your problem is also probably pH related, and possibly low light as well. T-5's are suitable only a few inches away, so 2' is too far for anything but a slight supplemental light boost. 

[Jay]

Jon,

I thought adding acid raises the PH.

Jon Parr said:

Robert, pH is way too high for your plants, and your nutrient uptake is most certainly impaired. Lower it and you'll be amazed. I prefer HCl (muriatic acid), and lower slowly. To estimate how much acid to add, remove a measured portion of water and experiment with a little acid and monitor it's effect, then calculate a dose for the whole system based on your findings. Common advice here on this forum is to not change pH more that .2 points per day. That's probably great advice, but it would take forever to lower hard water starting over 8.0, who has time for that? I personally haven't had a problem with an immediate fluctuation of 1 or 2 points lower after just a few minutes of circulation. Ive even done some foolish doses that lowered pH from 8 to 4 in five minutes. Crazy! And my pangasius catfish were freaking out, running into glass, burrowing into gravel, jumping out of the water. The tilapia and redclaws in the same tank were completely unaffected, just business as usual. Even so, the pangasius recovered and no fatalities. The next day the pH had rebounded to 7.9, and this is a normal and expected phenomenon. The acid needs time to balance the bases, and an immediate reading will not be accurate. Anyway, test your pH, record, add a little acid, after a few minutes of circulation test again to make sure you didn't overdo it, then ignore. Test again the next day at the same time (daily CO2 cycles will cause the pH to swing daily about .2-.4 points or more, lower in the morning, higher in the evening, so test and record at the same general time each day). Likely the pH will have returned to previous day's level, or slightly lower. Record, add a little more acid, ignore. Repeat this process daily. At some point it will start to drop. As it does, the same dose of acid will have more and more affect on pH, so be careful not to overdo it as you near your target pH. Once it gets there and holds for a couple of days, you are golden. Your plants will thank you with an explosion of growth. In a healthy, aerobic system, the pH will drop a little every day. That's a fact. That is why some folks need to add a base like KOH or a carbonate like oyster shells in order to counter-act the acidifying affect of nitrification. Why, you ask, is your system still 8.0 after being "well seasoned"? Good question, I'm glad you asked. Because the nitrification process is mildly acidifying compared to the base components of hard water, and regular top-up water adds more base to the slow battle that the bacteria are fighting. Once the bases are neutralized with your HCl acid, then the nitrifying bacteria can begin to win the battle. Depending on your particular water chemistry, you may have to add something to your system to keep the balance. So far for my big system, less than 2 months old now, the pH will drop to about 6.0 before needing to be topped up. My well water is currently 8.8, and this hard water is all that is needed to buffer the water back up (actually I still need a little acid if transpiration is high, meaning more hard water per unit time). It originally took about 2 gallons of 14.8% HCL to bring 2200 gallons of total system water down from high 8's to high 6's over about a week's time, and maybe a quart since then to fine tune. To make this all more confusing, my well water will soften as the rains fall, to about 7.0 by spring, then harden up again as the dry season ensues. So, I will have to adjust my regimen as the seasons change. 

Kevin, your problem is also probably pH related, and possibly low light as well. T-5's are suitable only a few inches away, so 2' is too far for anything but a slight supplemental light boost.