Aquaponic Gardening

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Hi

I am considering buying a roll of 800 gauge high density polyethylene to line my growbeds, is 800 gauge heavy enough?  i'll be using pea gravel as grow media,a roll of (HDPE) is very expensive,  i want to use plastic or rubber pond liner but i was concerned about the plastic leaching into the water!,  does rubber leach?  would leaching in ap systems gb or ft liner's hinder AP farmers from obtaining an organic cert?. thank you.

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I've probably already said this but...

Depending on "food safe" ratings for plastics does not necessarily make them BPA free. I want to avoid BPA in the AP system so I tend to go for the HDPE plastics. Unfortunately there are lots of great HDPE materials out there which are probably just fine though they don't have a "Food Grade" rating, like stock tanks.

You mention a web site with more info about BPA but what about the PVC?

Now I know there can be not so "safe" stuff in some of the flexible PVC liners (the plasticizers that keep them flexible are the questionable chemicals) but so far I've never found any evidence that the rigid pvc drinking water pipe or fittings have anything nasty to leach and I have done some searching. If you have any links to more info on the PVC please share.
Hi tc,

I have already shared the link, ( ScientificAmerican.com) entitled (Like a Guest That Won't Leave, BPA Lingers in the Human Body) "That may explain why 93 percent of Americans carry BPA in their bodies, according to the CDC, or it could be that exposure is coming through different routes than food, such as the polyvinyl chloride (PVC) pipes often used for water lines in modern homes".
I honestly dont know what to believe, so im going to stick to hdpe all round.

Best wishes.



TCLynx said:
I've probably already said this but...

Depending on "food safe" ratings for plastics does not necessarily make them BPA free. I want to avoid BPA in the AP system so I tend to go for the HDPE plastics. Unfortunately there are lots of great HDPE materials out there which are probably just fine though they don't have a "Food Grade" rating, like stock tanks.

You mention a web site with more info about BPA but what about the PVC?

Now I know there can be not so "safe" stuff in some of the flexible PVC liners (the plasticizers that keep them flexible are the questionable chemicals) but so far I've never found any evidence that the rigid pvc drinking water pipe or fittings have anything nasty to leach and I have done some searching. If you have any links to more info on the PVC please share.

Hey Kevin & TC, thanks for that info.  Yes, I'm aware of BPA and I definitely plan on avoiding it in my system!

 

I wanted to get back to the HDPE stock tank question, since I think I've just changed my mind and now plan on going with LLDPE tanks from Behlen (http://www.behlencountry.com/files/Tanks%20&%20Waterers.pdf ; see p.4; I called Behlen and was told they are LLDPE, I had read at various places online that they were HDPE, not true).  These are made of FDA food grade, UV-stabilized LLDPE, and I like the dimensions of the long 3'x2'x8' tank.  These also come with a 3-year warranty whereas the RMs come with only 1 (though of course I will be voiding the warranty right away when I start drilling, still it's good to see how confident the companies are with their products).  The biggest advantage I see with them though is that modern LLDPE is just about as strong as HDPE, but much more flexible (HDPE is very strong, but quite brittle).  I've been reading stories of people's HDPE bins cracking and I really want to avoid that, sounds like patching them can be quite difficult.  I should say though, that a lot of the RMs (HDPE) ended up cracking after lots of use of their drain plugs (also animals stepping in them, or letting water freeze in them).. I doubt you will ever touch the pre-fab drains in AP use, so these could in fact hold up for a very long time before cracking (barring bulging roots or freezes).

 

From what I can tell the chemical resistance of LLDPE should be totally fine for an AP system, even though LLDPE isn't quite as resistant as HDPE.  I don't plan on storing crazy chemicals in the tanks. 

 

Is there any reason I should avoid LLDPE?

 

To relate this a bit to the questions above on PVC, see this comparison of LLDPE vs. PVC (for geomembranes, at least) : http://www.poly-flex.com/faq.html :

 

"What are the advantages of LLDPE over PVC geomembrane?

The advantages are as follows:

  • LLDPE has resistance to a wider range of chemicals as compared to PVC.
  • LLDPE is immune from biological attack by microorganisms. Microorganisms could attack PVC and use the plasticizer as a source of food.
  • LLDPE is resistant to burrowing animals, PVC is not.
  • LLDPE retains its physical properties due to long-term soil burial. PVC's physical properties diminish in time due to loss of plasticizer.
  • LLDPE is resistant to ultra-violet light, PVC is not.
  • LLDPE remains flexible at temperatures well below freezing at -25°C. PVC loses its flexibility and becomes brittle at -25°C"

 

The only feature I don't like is that these Behlen tanks have a molded-in aluminum drain plug fitting (which actually sounds like it would solve the RMs' main/drain problem).  I asked the Behlen guy if the aluminum would be in contact with the water, he said barely at all if you have the plastic drain plug screwed in.  Still, I'd prefer to have no contact at all, so I may add a bit of silicone caulk to that area on the inside of the tank  Necessary?

 

Finally, do catfish prefer round tanks or longer tanks, more like raceways?  I'm now thinking of using one of these 300 gal 3'x2'x8' tanks as my FT as well.  I'll be raising catfish so I don't have to heat the water.

 

For a fish tank I think these might be just fine.  My first season I had catfish in a longer narrower tank and they seemed to do ok.  This year I have them in my new big tall round tank and in the 300 gallon rubbermaid tank.  can't say I notice much difference.

 

With the shallow tanks you will have to figure out a good cover to keep fish from jumping out.  Catfish will jump if the water level is near the top of the tank they can easily clear 4".

 

As to using the tanks for grow beds with gravel.  I think the flexibility will turn out to be a drawback.  See the gravel pushes out and doesn't let the tank flex back in the way it would with only water so over time gravel + water makes for more bulging than water alone.  This is why most gravel bed designs have lots of ribbing when they are made of the lower density stuff.  Even HDPE will bulge some when you go using it as a gravel bed and you may have seen my pictures of the small crack that the monster banana caused.  By the way, HDPE can be heat welded to repair such a crack but I simply used some aquarium silicone since it is only just up near the high water line in that bed.

 

Chances are the aluminum is not going to be a big problem but I think a coating of aquarium safe silicone left to cure over the metal before putting the tank in service is a good precaution.

 

I don't personally like the PVC liners because they do tend to get brittle with exposure to sun.

Rigid PVC is completely safe.  Flexible PVC has pthalates added to make it flexible.  These can be dangerous if they leach.  PE is generally pretty safe.

kevin darcy said:
Hi tc,

I have already shared the link, ( ScientificAmerican.com) entitled (Like a Guest That Won't Leave, BPA Lingers in the Human Body) "That may explain why 93 percent of Americans carry BPA in their bodies, according to the CDC, or it could be that exposure is coming through different routes than food, such as the polyvinyl chloride (PVC) pipes often used for water lines in modern homes".
I honestly dont know what to believe, so im going to stick to hdpe all round.

Best wishes.



TCLynx said:
I've probably already said this but...

Depending on "food safe" ratings for plastics does not necessarily make them BPA free. I want to avoid BPA in the AP system so I tend to go for the HDPE plastics. Unfortunately there are lots of great HDPE materials out there which are probably just fine though they don't have a "Food Grade" rating, like stock tanks.

You mention a web site with more info about BPA but what about the PVC?

Now I know there can be not so "safe" stuff in some of the flexible PVC liners (the plasticizers that keep them flexible are the questionable chemicals) but so far I've never found any evidence that the rigid pvc drinking water pipe or fittings have anything nasty to leach and I have done some searching. If you have any links to more info on the PVC please share.

Thanks TC.  

 

Your concern about the flexibility gave me pause, I agree that too much would be a con.  But I think having more flexibility than HDPE, without too much bulging/tipping, could be a great feature over the long run, at least in terms of cracking.  I'm about to visit the feed store to see one of the Behlen poly tanks in person.  Hopefully they also have RMs for me to compare with.  Their catalog states 'All round-end [poly] tanks have an extra heavy duty, molded rim and an extra-deep sidewall rib design for additional strength'.  So they make them sound pretty tough.  I can definitely tolerate some bulging, especially if it affords me more crack resistance, but I do have to be convinced that a GB will more or less hold its shape over time.

 

I see your point about the F/D cycles causing the gravel to settle and the bulging to worsen over time.  It seems like this would be more of a concern with small gravel that can easily be moved around and settle more tightly together/bulge out more.  Of course all gravel will settle/bulge, but I think using larger gravel would help.  Do you think?  I'm currently planning on 1-3" river rock in the bottom 1/3 of the GBs, then 1" rock for the rest.  

 

The question is just how rigid is the LLDPE tank design, can it handle the bulging of bigger rocks?  I'll let you know what I think after seeing one in person.  If only they would let me fill one with gravel!

 

Has anyone here seen the Behlen poly tanks in use as gravel GBs?  Or any other (L)LDPE tanks as GBs?

 

It's good to hear that your catfish were just as happy in your narrow tank as in your round one.  I guess I already know the answer to this question, since I know you use a 300 gal RM for a fish tank (which are 25" deep), but is 2' (I would probably only have ~20") really deep enough to keep catfish calm/happy?  I will have a good cover on the tank.  I don't want to stress them any more than necessary.

 

The stock tank does seem to be deep enough to grow fish out but I haven't actually grown any out big yet in water less than 24 inches deep.  The 20 inch water depth in the RMST seems ok to me so far but I haven't been using it for a full grow out yet.

 

JT has used some of the 110 gallon tough tubs as fish tanks and since I know they have quiet a bit more flexibility to them I asked what he thought about using them for grow beds and the impression I got was "probably not."

 

Now in my situation, the things getting brittle from cold is not a worry and I kinda doubt that using a more flexible tub would really have made an improvement to my banana situation, I can just imagine what would have happened if the bed were to have bulged more.

 

Anyway, you will have to make your own call as to if LDPE or HDPE is better for your situation, both are fairly safe as far as any leaching goes.

I went to see a few tanks in person.  The Behlen tank I was told was LLDPE had a company sticker on it saying 'High Density Polyethylene', so now I don't know what to believe.  I may call the factory again.  Anyway I think these tanks are indeed too thin for long term use as gravel-filled GBs.  I can see them bulging/straining under all the weight, especially in the summer sun.  I may still use them for DWC tanks and FTs, mainly because I like the 3'x2'x8' (300 gal) dimensions, but I'm not sure.  I checked the aluminum drain plug and it doesn't look there would really be any contact with the water.  If so it would be only a tiny area to coat with silicone.

 

The RMs are at least twice as thick as the Behlens, if not 3x.  They have a clear HDPE stamp on the bottom.  I figure if I never mess with the drain plug or move the tanks they should be good for 5-10 years, barring deep freezes or lots of root pressure.  I'm going to go with the 150 gal tanks to give bigger roots more room.  I was also thinking of getting a 300 gal tank for trees, but I'm not sure that's the best idea (vs. two 150 gals).  Any tree growers have an opinion here?  I wonder if that much gravel would be a problem for this plastic.

 

I also saw one of the Tuff Tanks TC mentioned, I think it was LDPE and quite thin, the most flexible tank I saw.  And I saw one of the High Country tanks, I forget what plastic it was but it was a decent thickness and just a little bit flexible.  It was very similar to the Behlen tank (I may have read somewhere that they're made in the same factory?) but ~twice as thick.  Very nice but I think probably still too flexible for gravel beds in hot sun. 

If you do go for a 300 gallon tank for trees, you just need to have good support under the tank, that is a lot of gravel.  Keep in mind that it will be really difficult to reach to the middle of the bed to tend anything.

Yeah, I think I'll go with two 150 gal RMs for the tree experiments.  You're right, if I did get a 300 gal GB and later decided to use it for other things, it would definitely be a pain to work in.

"The stock tank does seem to be deep enough to grow fish out but I haven't actually grown any out big yet in water less than 24 inches deep. The 20 inch water depth in the RMST seems ok to me so far but I haven't been using it for a full grow out yet."

Ive grown Tilapia from fingerlings to 2+ lbs in the 110gal stock tanks so you shouldnt have any problem TC. Cats just like more bottom surface area so you wouldnt be able to grow out quite as many. You can mix them with Tilapia in the warmer months though (read about your past experience)if you need more nutrients out of the tank. Ive got 10 1-2lb cats in one of my other 120 gal tanks with about 18" of water in it (slightly larger surface area then the rubbermaid stock tanks) and they are fine. I have them in a mixed tank and they lay all up on each other in a tight little group, weaving in and out like snakes or something. The bass roam around the tank in a little school and the few crappi I have left hold tight to the koi b/c he's the biggest thing in the tank. They all get along great though, very fun to watch. Im pushing the weight limit in the tank but I don't feed heavily so I can still keep parameters in check. Im actually pushing the weight in all my tanks right now...about time for a fish fry :)
great to hear Ryan, thanks.

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