Flood and Drain Cycle and Tomato Growth

[MoeCanada]

Hi All,

I had few questions. I started two aquaponics systems. one is 5 weeks old and one 8 weeks old. The one 8 weeks old had a consistent PH of 7 throughout. I planted basil,Lettuce, peppers,beans,sweet peas,mint,eggplant and tomatoes. I have 50 gallon tank with about 12 rainbow trout. two growbeds 2' x1'x 6" . Lettuce did really well and i already harvested a few. basil did well too. snow peas and beans are flowering as well as producing pods. the eggplant and pepper are a little slow but reaching there but my tomato plants keep dying. I planted another batch three weeks ago but same problem, they start good but after about ten days the new leaves start turning yellow and then the growth slows down and then the older leaves turn yellow and whole plant becomes white except the stem that stays green. I added chelated iron but nothing happened. My flood cycle is 11 mins to flood and 1 min to drain. My questions are:

1. Do you think it is happening because my growbed is not mature ?
2. Or my Growbed not deep enough
3. May be because of the water being cold as it is 15C ( i don't know if tomatoes like warm water)
4. Or My flood and drain cycle being too quick
5. Or is it Damping off disease
6. Or is it some kind of nutrient deficiency

Any help would be greatly appreciated as i planted about 20 of them and all ended up with the same fate. Thank you

[Molly Stanek]

I have come across a similar problem with some otherwise healthy plants and I have assumed that it was water stress after reading a lot to try and diagnose it.  I am wondering if setting your system to flood less often might help.  Of course, it sounds like you have already figured this out, so this is probably not even relevant!  :)

[Harold Sukhbir]

Hi Ted, just wondering.....are your nitrates building? 

Ted J. Hill said:

Hi Sylvia, right now the system is skewed more towards fish health than nutrient uptake; my target pH is the optimum pH level for nitrifying bacteria (a pH below 7.0 will reduce the activity of nitrifying bacteria, and at a pH of 6.5, Nitrosomonas growth is inhibited, pH for optimum growth of Nitrobacter is approximately 7.3 - 7.5 according to the literature I've read) and I've found this level helps me keep the ammonia and nitrites close to zero; but that's an inherent problem in AP, the pH that's best for the bacteria (and the fishies) isn't the best pH for the plants, that pretty much started my research into foliar feeding; I'm sure there is a "happy medium" for each AP system depending on the fish stock and the veggies grown, and that's one of the challenges of AP, does my biofilter still work and are the plants thriving <g>

 

Sylvia Bernstein said:

 

Good morning!  Ted, you are going to want to steer your aquaponics pH closer to a 6.5 - 7.0 range.  That is actually where you will see the best nutrient uptake (i.e. the most "green-ness" according to your chart).  Above 7.5 you are definitely challenging iron, and, even worse, you are challenging phosphorus which is a macro nutrient.

[Harold Sukhbir]

HI Ted, high nitrates are responsible for fish diseases, so keep a close eye on the readings. I hope you're not far from commissioning so that you won't have to keep chucking all those valuable nutrients!

[Harold Sukhbir]

Hi Ted, see you know your stuff! Well, high nitrates, above 40ppm, won't actually cause diseases, but stress the fish and so lower their resistance to diseases. I've read that at 60ppm most plants even start to die. Some symptoms are, fish become lethargic, reduce food consumption, slowed growth, and easily acquire diseases.

[Harold Sukhbir]

"I've read that at 60ppm most plants even start to die."

Have to make a correction here,Sorry these were notes on marine aquatic plants. Not sure what happens with fresh water plants. I do know that nitrates concentrate in vegetable fruit. Just hit me Ted, we are probably going a bit off topic here, won't want Sylvia to give me a spanking!

[TCLynx]

I've had nitrate levels way higher than 40-60 and they don't seem to phase my catfish or the plants.  Granted, I'm not trying to keep my catfish long term for breeding or anything.

[RupertofOZ]

In all my aquaculture studies, I've not been able to find any references to nitrates being a problem for fish at levels below 400+ppm... and that was for bluegill...

 

Harold Sukhbir said:

Hi Ted, see you know your stuff! Well, high nitrates, above 40ppm, won't actually cause diseases, but stress the fish and so lower their resistance to diseases. I've read that at 60ppm most plants even start to die. Some symptoms are, fish become lethargic, reduce food consumption, slowed growth, and easily acquire diseases.

[RupertofOZ]

Ted J. Hill said:

Hey Harold, don't forget the TAN, too (total ammonia nitrogen, NH3 and NH4+, plants can directly absorb ammonia-nitrogen as well as nitrate-nitrogen, having plants exposed to fish tank water actually reduces (somewhat) the amount of ammonia that your biofilter has to deal with . . .

That's true for aquatic plants, and duckweed is a perfect example... but it's not true to any significant degree in land plants...

[David Waite]

Moe I also want to comment on tomatoes. My ph never drops below 7.8 due to my brilliance in selecting a rock with a high ph. My tomatoes  are 5 foot tall at 13 weeks and are producing. I dont think ph is part of your problem. So far for me ph is not hurting me but peppers are another story. They hate my system. My water is very high in Iron as well. Thanks for the great updates.

MoeCanada said:

Thank you everyone for your help. Just to update on what happened to my tomatoes. The first batch just started good but then the new growth became yellow and stunted and the whole plant slowly slowly bleached. The same happened with the second batch but the miracle happened with the third batch and it started growing pretty good with lush green leaves and is growing lot faster than my potted tomatoes. Now the things that i have tried and did work for me, so i wanted to update everybody incase somebody has the same issue with tomatoes in the start.

1. Do you think it is happening because my growbed is not mature ?

This definately effects the growth of tomatoes as i build two systems for experiment sake and the new system is still having trouble with tomatoes but the older one which is almost 3 months now has started getting good growth
2. Or my Growbed not deep enough

I didn't change the depth of my growbed so at this point that was not effecting the growth of tomatoes.
3. May be because of the water being cold as it is 15C ( i don't know if tomatoes like warm water)

This definately was another thing as i put trout in my new system and bought some tropical fish from petstore for experiment sake and raised the water temp to 24C and it did help a lot not only with tomatoes but pepper and eggplants as well which are now flowering
4. Or My flood and drain cycle being too quick

Flood and drain cycle is still the same so that had nothing to do with tomatoes not growing
5. Or is it Damping off disease

No.
6. Or is it some kind of nutrient deficiency

Ok this one is very important as i found that due to my high stocking density my system tends to drift down to ph 6.5 and i was adding hydrated lime to bring it up but in the last four weeks i didn't do that instead added crushed eggshells and let the system run at PH of 6.6 and i didn't have to add anything to the system. 

 

So in my experience with tomatoes three things are very important

1. Water temperature

2. PH ideal 6.5-6.9

3. System Maturity

 

In my newer system the PH is 7.6 which iam trying to bring down to 6.9 over a period of four days. Once it is at 6.9 i will plant a batch of tomatoes in the newer system to see how they will do and keep u guys posted on that progress.

 

Another thing as i wasn't able to get MaxiCrop here, i used another brand which is available in Local Hydroponics stores in Canada called " Mermix Seaweed" and is fish safe and healthy. I have used it with goldfish, bluegill and trout. Thank you all once again and i know iam new to aquaponics but still wanted to update what i have found useful till now.