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Hi all, I set up a 70 gal system less than 8 months ago and have 7 tilapia.  One of them is almost "ready for lunch".  So far we've harvested several tomatoes, lettuce, kale, shiso and such.  Cucumbers and peppers are trying, the plants just aren't producing, peppers are losing leaves and cucumbers develop cukes initially but they whither away.  The leaves on the plant indicate it may be due to a magnesium deficiency.  Today I plan to pick up some epsom salt but was also thinking of a general kelp based fertilizer to help out.  I know it's a new system and has just not had time to mature and develop the mineralization needed to support the more demanding fruiting plants.  The local home depot carries Alaska Pennington 32 oz. Pure Kelp Plant Food.  I would prefer to use something that's more of a known product (seasol or maybe maxigro), but I am new enough to AP that I'll feel better asking advice from folks here that have much more experience.  Even though this sounds like more of a plant topic, the reason I'm asking is that I want to buy/use a product that won't be harmful to the fish, especially since I have added a connected tank with about 250 fry from an unplanned pregnancy.  Advice?

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Kelp Fertz:  If it labeled all natural or organic, it should be OK.  Check the analysis, example 2-2-2 (nitrogen, phosphorus, potassium, to see if it is what you need.  Epson salt is widely used in ap.

on the note of cucumbers are the bee's able to polinate the flowers? if not you ill have to polinate them yourself. that is one of the symptoms of not being polinized. excuse my spelling. as far as the rest of your fertiliazation i will need to watch what others say like george did to learn myself.Happy Growin to Ya Wild Dog

I follow Bright Agrotech's recommendation of bi-weekly addition of Epsom salt, potassium sulphate, and iron chelate. Since I started this I haven't had any nutrient issues.  In my 500 gallon system I use 6 tsp. iron,  3 tbsp. epsom salt,  3 tbsp. potassium sulphate. If I need to raise the pH I switch the pot. sulphate with potassium hydroxide. If you want to try this just use 15%-20% of what I use in your 70 gallon system.

Thanks for the replies, fellas.  Wild Dog, I have been trying to pollinate with both a Q-tip and a small paintbrush, and neither method has had any effect.  The fact that the leaves are showing textbook magnesium deficiency symptoms (and add that to the fact that cucumbers are notorious for high magnesium consumption), I figure that even if I'm pollinating correctly the cukes can't develop.  Jeff, that seems like alot of iron for bi-weekly; what plants are you feeding?  If i even add 1/8 tsp of iron chelate it turns my water red for almost a week!

So I've added the epsom salt, and have diluted the kelp fertilizer for use as a foliar spray.  Since it's as George said, it is 'natural-based' and listed as organic, I'm not going to worry about overspray or whatever may drip off the leaves into the growbed.  I don't plan on adding it directly into the system at this point, though I may consider it in a few weeks if everything starts perking up from the foliar treatment and addition of magnesium.

I know what you mean about the iron. The first time I used it a long time back it did the same thing to my system even in a lesser dosage. But it doesn't seem to be affecting it like that now. Maybe I have a little more water than I think or the GBs are sucking it up. I have lots of tomatoes and some greens in the beds. 2 IBC beds and 1 IBC raft and 1 IBC fish tank with a LOT of fish lol.

In my experience, most cucumber varieties are self pollinating, so I would doubt that pollination is your issue....

My favorite place for kelp powder currently is kelp4less. It's cheaper since it's sold dry and it has good potassium content.

https://www.kelp4less.com/shop/kelp/

Alex,  Let me first caveat right up front that I am absolutely not any kind of expert in botany/horticulture.  I grew up on a farm (planted crops and tended livestock) and that's about the beginning and end of my expertise.  I am learning by asking and by researching for myself.  I have learned that there are many varieties of cucumbers that are listed as "self pollinating", which means it has both male and female flowers appearing on the same plant.  The ratio of female to male blooms in 'natural' varieties display a minimum of a 3:1 ratio, most varieties carry a 9:1 ratio but 12:1 ratios are not unusual (with the female (fruiting) flower in the majority).  The female flower still requires the pollen from the male flower for fertilization.  From this I infer that the term "self pollinating" simply means that the potential exists for a fortuitous breeze be all that is needed to allow this plant to produce cucumbers.  There is no need for a second plant to provide 'cross pollination' capability.

There are specifically (genetically) developed varieties that may even present a 30:1 female/male flower ratio, but it seems to me that ratio would absolutely rely on active pollination of some kind, especially considering that male flowers usually appear about a week ahead of the female and start closing about the same time the female bloom is opening....pretty small window of opportunity if I'm reading it correctly.  There are even some designed to grow only female flowers, but these are generally packaged along with cucumber seeds that produce a plant with predominantly male flowers to be planted amidst the female plants.

The only cucumbers I've read about that don't require pollination any kind are called Parthanocarpic Cucumbers.  These have been developed for greenhouse growing (insect-free zone).

Whew... apologies for all that.  I tried to summarize as best I could.  My problem is that I haven't seen a bee in months, and no more than 2 or 3 butterflies in the last couple months.  I may have to start growing lavender or something just to encourage bees to come around.

If any of the ramblings above are incorrect, please (anyone) provide correct information.

I have looked at kelp4less and have saved their site to my favorites.  Thanks for the tip!!

Yep, that's correct. I'm growing a parthanocarpic variety myself. Makes it pretty easy. What variety are you growing?

BK, You used my opening line to most of my posts, "I am not an expert". All most of us do is share what we have read, seen, and experienced in hopes that it will help someone else. Thanks for the effort you put in to sharing all that info. BTW my cucumbers are on their own for pollination.

Alex, I am growing Japanese cucumbers.  They are self-pollinating, except that pollination is not happening without my intervention and even then I am still seeing the ovaries whither away. Perhaps the mineral deficiency hasn't been addressed at the cellular level yet (it's only been a couple days).  The leaves are already starting to green up so hopefully we can get a few cucumbers from this plant before it's done.  All the other plants are responding as well.  Whether it's the addition of magnesium or the foliar kelp spray (or both) I can't say.  Next week I'll reduce the foliar spray and observe what happens.

I have a magnesium test kit on order (in the mail) so I can take a more definitive look at that nutrient.  I'm truly curious to see what the actual levels are since the General Hardness test goes off the chart.  I've seen some material that states that calcium, at very high levels, can block to absorption of magnesium. Any truth to that?

I've heard that it can also block potassium, although I've always been unsure about how exactly to apply those two tidbits of information. I switch over to rain water once the winter ends because I was tired of my water being so high in pH. Feels less complicated to just add the minerals in yourself, rather than trying to fix well water.

I'm pretty sure cucumbers like 15-30ppm of magnesium, which I believe comes out to around 1.5-3oz of epsom salt for a 70 gallon system. I've gotten better results adding it all at once or in two additions, rather than a teaspoon or tablespoon at a time. Maybe then see how long that carries you through until you see a deficiency again.

Also, nutrient deficient cucumbers can get pretty weak and end up extra susceptible to pests and powdery mildew; it can be hard to repair them if you don't catch it early enough. It probably wouldn't hurt to plant a couple extra ones for later if you have some extra seeds lying around.

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