Aquaponic Gardening

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This forum is proving to be VERY helpful. I now need help with a little bit of a mildew problem on my 50 gal grow bed. A few days ago I noticed that the leaves to my basil, mint and beans had some white spots on them and they seem as though they are slowly progressing because they are now small white patches. I also noticed that on the bottom of my 2 sage plants and at the bottom of one of my swiss chard plants (where the stem meets the hydroton) there was a--this is going to sound gross--fuzzy, white substance that I presume to also be mildew. I've always been told that mildew is gray or white and either powdery or fuzzy whereas mold is black, green, red, and blue and in plaques. This is why I believe my problem is mildew and not mold.


I think the mildew was using some of the dead/dying leaves as a fuel source and the moist hydroton provided a hospitable environment for growth. Note that there werent many dying leaves on either the sage or the chard, but just a few towards the base.


Do you think that my water level may be a problem? Due to algae concerns, I have made sure that the maximum water level in the growbed is at least an inch below the top surface level of the hydroton. My level is actually 1.5-2 inches below the top surface level. Is it normal for some of the top pebbles to be moist even though the water does not get that high? Pushing the standing pipe down to lower the water level further is a pretty big hassle at this point because the cap to my gravel guard is not unscrewable and would require me to remove all of the hydroton around the gravel guard, which is a huge pain! So I hope that this isn't the problem.

I removed the 2 sage plants and removed any of the detritus at the base of the plant, boiled the hydroton that was around those plants and replaced it. I have also placed a blowing oscillating heater (set on 80F) and a fan (set on low) that is blowing on the growbed to hopefully dry things up. I have a feeling, though, that the problem will return unless I completely erradicate the mildew problem. What is a VERY effective mildew treatment that won't harm my fish (e.g. neem oil, diluted hydrogen peroxide, potassium bicarbonate, and even milk!). Any help on this issue would be sincerely appreciated.



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I would do the potassium bicarbonate treatment as that can be effective on more than one level by changing the pH of the surface, it tends to help against the downy mildew/mold that is usually the fuzzy stuff and it can also provide the plants with a foliar feed of potassium at the same time which is a plus when fighting the powdery mildew and it can also help against some other fungal problems as well or at least I'm told.  And having it on hand can also be good for buffering your pH up when it starts to drop.


the powdery mildew is one thing, then there was the fuzzy mildew, now I just went to check my mint plant and I touched it and all these white specs came down from it so I looked at it closer. They WERE NOT moving at all so I thought it might of just been the spores or particles from the powdery mildew. But if you slightly blow on them they go up in the air and then back down--but not in a falling-dust-particle sort of way. Whatever this is seems to be able to control itself while in the air, as if it's flying; they might be white flies. I think I tricked myself into thinking it isn't an insect because I didn't see them crawling, but I mean they seem to fly. I'm clearly in denial about the fact that my aquaponics system is infested with this stuff. There's also these VERY SMALL green insects that crawl on the hydroton. I have only seem 3 of them so far, but where theres one, there's many. I know that some plants in my house a few years ago had aphids, but those seemed to be white and moved.  


I'm begining to have serious doubts about having an indoor system, at least in my house. I can't believe I am actually saying this because of how much I invested into this system so far, but I am actually contemplating about dismanteling it. I'm not a squeemish person when it comes to insects or mildew, but 4 unfortunate discoveries in one day just seems to be a huge problem and only a sign of things to come. I've already ordered activonate and potassium bicarbonate for the mildew problem, but I don't know what to do for these little mites--I don't even know what they are! Please, someone, knock some sense into me and tell me something that will help me!!!!!

These are the pictures of the powdery mildew and the white specs on/around my mint. I don't know what they are and as you can tell they are TINY. They don't move when I look at them but if I blow a little bit around them they shoot up into the air and look as though they are flying around. Spider mites? White flies? Aphids? Larvae? Powdery mildew particles/spores? (Hopefully the last option). I sprayed all my plants with a foilar spray that has composted guano and fishmeal in it. I know that worm compost is used to treat powdery mildew so I had this on hand so I figured I'd spray it on and it seems to at least hold down those white specs so they're not jumping/flying around. I had to spray something just to keep my sanity! The potassium bicarbonate is coming tomorrow and the actinovate is coming the day after--both are natural fungicides. What is a powerful, proven effective treatment for insects & mites that is safe for fish?? Please give feedback! Thanks!

Organocide. It sounds lethal, but is just oil, mostly soluble fish oil that you mix with water, spray on every surface of your plants, fights soft-bodied pests like aphids and mites, and mildew. Smells like fish for a while, but it's worth it. Oils can coat the gills of fish, so contain overspray and drips. I'm not that careful, and have had no problems.

Also, you can burn sulfur in a special boiling pot made just for that purpose from hydro stores. I have never used sulfur with fish present, but I am burning a pot tonight as I type. I'll post again if there are any problems. Sulfur also discourages mites, and extremely effective on killing and preventing mildew and fungus.

Also, and I can't remember if I read this or I'm making it up, but generally bacteria and fungus fight each other. So spraying a hi-count fungus liquid combats bacterial problems, and vise-versa. Worm tea is highly bacterial, and is a good foliar spray anyway, and would likely combat mildew.


Pottasium bicarbonate works best as a preventative.  Once the problem is established, I've had good results with it if I stayed on it.  By that I mean applying the KHCO3 solution full strength using distilled or R/O H2O, then the next day use 1/4 strength (this will rinse the heavy residue from leaves while still keeping the pH alkaline enough to be effective).  Repeat this, and don't miss a day until the problem is gone.  Lightly spray the growing media (grow rocks / LECA) with each application as well and keep an eye on your fish tank's pH.

Potassium Silicate is another thing you can try.  The potassium will increase the alkalinity of the leaf surface, getting rid of the pathogen(s), while both the potassium and the silicate will both help strengthen the plant's cell walls to ward off attacks in the future.

Avoid spraying under full light or intense heat, but also don't spray in the evening as it will keep things wet throughout the night.  Mornings or the beginning of your light cycle are best.

I can't tell from the photo, but if the white specks you're referring to jump rather than fly, then it may be springtails.  If they fly around, my guess would be that you have a common problem  -fungus gnats.  Springtails  and fungus gnats love moist soil/ growing media.  Spider mites don't fly or jump.  

If you can get a better picture of the critters, I could probably help identify them.

Another alternative is a full cream milk spray... 1 part milk to 9 parts water...

P.S... it's the "silicate" that increases the alkalinity.... not the Potassium...

Ooof, thanks Rupert  - you're right, that statement didn't make sense.  I tried to copy, paste, and edit from a comment I left on another site...  that's what happens when I try to post from my phone.  

I also don't normally mention potassium silicate in regard to aquaponics because so many are concerned with silicates in aquaculture and I've actually been scolded for bringing it up in the past (another topic that needs discussion and clarification...).

A 10% milk solution works well, but in a greenhouse or indoor environment it leaves a sour smell that I'd rather do without .  

Yep.. there's that...


Jesse Hull said:


A 10% milk solution works well, but in a greenhouse or indoor environment it leaves a sour smell that I'd rather do without .  

I had mildew in the beginning with wet pebbles and I think you will find a fan should solve the problem. Now they are dry an inch below the surface. It may take a bit longer for mildew to go away, but air flow will work against it.

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