Plants look sickly in early phase, pH keeps dropping

[David Mitchell]

My plants need help and I am not sure what to try next.

I just have a tiny trial AP system from which I am trying to master the basics: 10 gallon tank, 10 gallon hydroton/lava rock grow bed, flood and drain setup with external loop siphon that maintains a 3-5 minute flood/drain interval.  It is working great.

It is at day 31.  Cycling went fine, it seemed.  Ammonia and nitrites consistently dropped to zero after daily additions of ammonia.  So I added fish about 1 week ago.  I only placed 4 small gold fish as a trial.

As far as plants, at the beginning I transplanted some cilantro seedlings I had grown in soil after rinsing off the soil.  They looked really good for a week or so, then began to turn yellow and dry looking, and now they are withering away.

I also broadcast-seeded cilantro, basil, peas, and cucumbers simply as a trial, to see how well things would germinate.  The cilantro came up nicely and looked good, but has now stagnated and some sprouts have withered.  The leaves have not yellowed, but it just isn't growing much.  The basil sprouted as well and some seedling look healthy but are growing very slowly, while others have withered.  The peas and cucumbers I planted last, and they are just coming up now.  The cucumber cotyledons have a bright yellow ring along the edge of the leaf, suggestive of some deficiency, I assume.

Other cilantro plants, from earlier, that I had instead kept potted in the soil and under LED grow lights are now tall and bushy.

My pH has consistently drifted down around 6.2-6.4 despite corrections.  I usually slowly bring it up to 6.6-6.8 if I can, with KOH.  The ammonia is at 0.25 ppm today, nitrites are zero, and nitrates are 5 ppm.  I have added a 1/2 cup mesh bag of crushed oyster shells, buried a few inches under the grow bed at one spot without plants, to help with carbonate buffering capacity.  

In hopes of helping the plants, I tried spraying some foliar feed (diluted as directed from a hydroponic general formula feed), and I also added Maxicrop once at recommended dosing to the system this week.

Still things look sickly.  I've attache pictures of one original cilantro transplant and one cucumber sprout with the yellow edges.

Am I missing something?

Is it reasonable to add a general hydroponic nutrient solution to the system for a short time, and then see if a new equilibrium is reached.

Two things that puzzle me: plants dying and pH dropping every day

Any help appreciated.

[Keith Rowan]

how deep are you flooding the growbeds?  the top layer of media looks a little wet, it should be dry.. flood to a but under 1" below the surface of the gb..

what are you using for a light source?

what are you feeding the goldfish?

 

[David Mitchell]

It floods to 1-2 inches below the surface.
But I've been wondering if it cycles too frequently. My pump is too fast for the system I think, and maybe it would be better to have fewer cycles per hour. To keep it drier.
My lights at T5 x 4 x 48-inch
I've started by just feeding the goldfish goldfish food, but the problems predated the fish being started.



Keith Rowan said:

how deep are you flooding the growbeds?  the top layer of media looks a little wet, it should be dry.. flood to a but under 1" below the surface of the gb..

what are you using for a light source?

what are you feeding the goldfish?

 

[Alex Veidel]

You should usually aim for 10-15 minutes for a flood and drain cycle. If it's too fast, you can always divert some of the water that your pump is carrying back to the fish tank for extra aeration.

David Mitchell said:

It floods to 1-2 inches below the surface.
But I've been wondering if it cycles too frequently. My pump is too fast for the system I think, and maybe it would be better to have fewer cycles per hour. To keep it drier.
My lights at T5 x 4 x 48-inch
I've started by just feeding the goldfish goldfish food, but the problems predated the fish being started.



Keith Rowan said:

how deep are you flooding the growbeds?  the top layer of media looks a little wet, it should be dry.. flood to a but under 1" below the surface of the gb..

what are you using for a light source?

what are you feeding the goldfish?

 

[David Mitchell]

How does the wetness issue get resolved in systems where the plants are floating in the nutrient solution? It seems that if this is the problem, those systems would also fail. Puzzled. I'm glad to try anything, though.

[Steve R]

Have you tested your Kh or alkalinity? It sounds like you have used up all of your alkalinity. Get a KH test kit from your local pet shop and tell me what your dkh is or alkalinity in ppm.  When you cycle a new system you make nitric acid that disolves your alkalinity and depletes it over time. It has to be added back or your PH will not stabilize. It is common when first cycling a tank to burn through it because of all of your high nitrate and nitrite and ammonia and you have to buffer it back up. Thats what it sounds like your issue is. The shells you added will help but not fast enough to save your plants you need to use potassium carbonate or preferably bicarbonate to get your KH back up. Let me know how that works out and if your still stuck well go from there but i'm more than willing to bet your KH is under 40 ppm.

[David Mitchell]

Ok, I'll give it a try.
But since plants prefer a lower pH anyway, would this drift down cause my plant growth problems as well? Is the alkalinity or buffering capacity critical for plant growth or just for a stable pH?
And what is the target range for alkalinity ppm?

[Steve R]

Even if they prefer low PH they want a stable low PH. Low alkalinity can absolutely effect plant growth. It can dramatically slow it down. In order to make a new cell the plant needs alkalinity, calcium, iron, potassium, and magnesium.  If any of these are outside of there ranges for cell production it slows down fast. You need a DKH above 4 preferably closer to 6 or 8   or 74 to 175 ppm alkalinity to be in idea range to maintain a stable PH. The lower your alkalinity the less stable your PH. You won't have a negative impact on your water until you get well past 14 dkh so over dosing is not an issue.  alkalinity is slowly consumed by your nitric acid from your nitrogen this is why it must be added regularly. For example if your alkalinity is below 30 your PH can move by as much as a full point in as little as 14 hours. That fast of a PH change is REALLY hard on almost any living creature aside from certain kinds of fish.

[David Mitchell]

Thank you. I will be checking alkalinity soon. And potassium carbonate is the easiest option? This is what is found in pH Up for hydroponics, correct?

[Alex Veidel]

In systems where there plants are floating in solution (i.e. raft or nft), wet surfaces are designed to have limited exposure to light. In a raft system, your rafts float on the water and block most of the light. In a grow bed, the entire surface is exposed to light, which promotes massive algae growth. Algae steals nutrients from your system and can cause pH swings, so it's best to keep it out as much as possible.

David Mitchell said:

How does the wetness issue get resolved in systems where the plants are floating in the nutrient solution? It seems that if this is the problem, those systems would also fail. Puzzled. I'm glad to try anything, though.

[Alex Veidel]

True, plants like low pH. But your fish don't, and neither do your nitrifying bacteria. Nitrosomonas and Nitrobacter like pH levels of 7.0+ so having a pH below 7.0 slows down your cycling process significantly. Ideally, try to keep your levels at 6.8-7.0. And you can use General Hydroponics pH UP to raise your system's pH. It's a good product.

David Mitchell said:

Thank you. I will be checking alkalinity soon. And potassium carbonate is the easiest option? This is what is found in pH Up for hydroponics, correct?

[David Mitchell]

So, I was able to adjust my pump rate down a little, but now at the slower rate, the siphon won't kick off (it just dribbles), so I may need to change the caliber of my loop siphon tubing, I guess, unless there are other tricks.

Alex Veidel said:

You should usually aim for 10-15 minutes for a flood and drain cycle. If it's too fast, you can always divert some of the water that your pump is carrying back to the fish tank for extra aeration.

 

[Steve R]

As long as your PH is above 6 your cycle should be unaffected. I regularly cycle tanks all over the 6 PH range for discuss, and other low PH fish in breeding tanks. There is bacteria that can cycle cold water and most PH ranged its just weather or not you have it but 6s shouldn't affect cycling all that much.