Mold forming on hydroton in floating raft system

[Dion Manly]

Hello,

I have a floating raft system with hydroton in net pots.  Since I started the system about five weeks ago, I have had mold developing (at least I'm pretty sure it's mold) on the top layer of hydration in the net pots.  

 

I went to a local hydroponic store and they thought the problem may be related to light hitting the top layer of hydroton, or low DO levels, so I purchased some covers for the net pots, and added air stones to the grow bed.  I tried removing the top layer of hydroton from each net pot, but the problem came back after about a week.  

 

I've attached a picture of one of the net pots.  I have noticed that the problem seems to the worst closest to the point where water enters the grow bed.  I have several things growing here, strawberries, celery, cilantro, parsley, etc.  Oh, and the water level comes just about to the top of the hydroton.  Any suggestions to get rid of this problem?

 

Thanks!

Dion

[Jon Parr]

It looks like salts buildup from the picture. If so, you may have hard water, probably not a problem. Do you use any hydro nutes? If so, keep your ECM numbers good and don't worry. Salt buildup will be heaviest just above water line near splash zones and bubble zones, like your water inlet. Light discourages mold, but encourages algae. Plants ok? Might want to test your water chemistry.

[Eric Warwick]

I have had a similar problem in my deep water culture system (hydroponic) , after I put it through normal 3% hydrogen-peroxide it went away. I'm not sure if it's safe for aquaponics, though, because of the fish.

[TCLynx]

That looks like minerals to me too.

Here just so you know you can use the image button (second from left on top of the text box) to put pictures directly in your posts so people don't have to click away to see what you are talking about.

Anyway, If you can get the rafts to float higher to the top of the hydroton isn't getting so wet you will probably be far better off on many fronts (will reduce algae and fungus by keeping the surface of the media dry.) If your water is incredibly hard you may want to alternate your topping up with some rain or RO water instead of the tap or well water.

I do not recommend using any hydroponic nutrients in with fish!!!
I do not recommend sterilizing an aquaponic system in any way if you have fish in it or a bio-filter functioning unless you are starting over (in which case you remove fish/sterilize/then re-cycle up the system then put fish back in.)

[Jon Parr]

I agree, TC. I have hard well water, and when everything was new I had some salts buildup. I didnt do anything to correct it, and eventually it went away. I assume the plants take up the hard water salts as fast as I'm adding them. I'm sure that the types of minerals that make the water hard may change individual results. I mentioned nutes, because there was no mention in the post about fish, could be hydro system for all we know, and for the record I have used flowering nutes in AP gardens with no harm to my tilapia. My tilapia are from the Salton sea, and are ok from fresh water to saltier than the ocean, as long as the shift is gradual. Also, hdrogen peroxide is pretty safe. A large dose would certainly disinfect the system and probably harm the fish and at least require cycling again. However, used as a spot disinfect is fine. It is powerful at the source, and harmlessly dissipates into fish water, with no residue. I have read that some fish can be transported with H2O2 on the water as an alternative to pure O2 above the water. Also, houseplants that are water logged, can be saved by dumping in some H2O2 because it carries oxygen thru the water to the roots, without harming the plant. I soak my pumps and pipes in H2O2. It nukes the algae and bio-slime, and is safe to drop back into the tank

[TCLynx]

The hard water is generally fine for most types of fish we grow in aquaponics, it is just in situations with huge amounts of calcium carbonate in the tap water you might wind up with very highly buffered water and a pH too high for plants to thrive.  It is for those kinds of situations that Rain or RO water might be recommended.

 

Being an Aquaponics Site I kinda sorta assume fish unless stated otherwise.

 

I'm cautious about saying fertilizers are safe to use.  I would be very specific about exactly what you used and at what concentrations.  (People sometimes skim read and from your above post might pick up the wrong bits of info and then go dumping in a strong dose of something and wind up in trouble.)

 

Just as long as the people reading understand the appropriate H2O2 dilution or usage to keep from killing the bio-filter or fish.

[Dion Manly]

Sorry for the slow response, but thanks for all the help everyone!  I'm relieved to learn that it is mineral build-up rather than mold.  (And thanks for the image tip TCLynx, I was wondering about that.)

 

This is an aquaponics system, I didn't even realize hydroponic folks were one this site as well.

 

As of September 10, the water quality in the system was as follows:

pH 6.8

DO 11 ppm

Ammonia 0.25 ppm

Nitrites 0 ppm

Nitrates 40 ppm

Water temp averages high 80s to low 90s.

 

Right now I have 5 goldfish in there, but soon I plan to use this as a holding place for tilapia fingerlings.  The fish tank is about 20 gallons, and the grow bed holds about 28 gallons of water.

 

The plants seem to be doing fine for the most part.  Oregano and thyme don't seem to like this system for some reason though.  Oregano grows well in my other flood-and-drain hydroton-based system, and I'll try the thyme there soon.  

 

The mineral build-up seems to be slowly taking care of itself.  I'm going to try raising the level of my plants slightly above the water level with another raft on top of the existing one.

 

Thanks again!

Dion