Questions about a system like at Growing Power

[Lance_Green]

Today was my first day as a volunteer at a non-profit urban farming group.

The aquaponics part seems to be copied from Will Allen's "Growing Power". It is in a greenhouse. Two grow beds, one above the other, with a four foot deep fish tank underneath. Fish are blue tilapia.

The flow pattern is constant flood. Water goes to top gb, which slants to drain at far end. Drains to lower bed, with lower bed draining to fish tank.

I read Will Allen's book, but it did not get into any technical issues of design.

The GBs are about 6 inches deep, filled with pea gravel. Watercress has been growing. The top bed is being redone.

There are worms and snails in the pea gravel media. From my understanding, worms are good. How about snails? Should the pea gravel be thrown away to get rid of snails or are snails good or maybe irrelevant?

I thought having the fish tanks under the gbs seemed to be an inconvenient place. There seems to be a concern about the fish tank getting too much sunlight. Apparently they had another tank in the sun and algae grew that was not eaten by tilapia. How do you feel about having the sun shine into fish tanks?

[bsfman]

Apparently they had another tank in the sun and algae grew that was not eaten by tilapia. How do you feel about having the sun shine into fish tanks?

My tank is in full sun and the water is crystal clear. No algae issues at all.

[bcotton]

Lance,

Most people's experience in this group is going to be systems much smaller than the one you describe. Some of the information will relate, some may not.

Personally, I like snails. I intentionally seeded my system with them. When they fall into the fish tank or sump they become fish food or cray fish food. Some types of snails may try to eat your plants or in raft systems they may try to eat your plant roots... I am not sure you are going to be able to safety get rid of them, they lay eggs and are prolific reproducers.

Some people worry about algae in the system but i never have. (I have the same philosophy about washing my grow bed media.. i just dont do it.) The pea gravel grow beds are going to filter the water from suspended materials and i dont see a problem with algae on the walls of the fish tank unless it's causing significant competition for nutrients?

On the other hand i prefer to be able to see my fish and the algae on the walls of my ibc's kind of cammo's my fish... So i have a couple of plecos that i use to keep the walls of my fish tanks clean... to my knowledge they are only helping me aesthetically and not functionally. I havent had any problems with the tilapia , catfish or perch bothering the plecos... They generally stay out of the way on the sides or bottom of the tank and they have a protective shell-like skeleton.

brian

[Parker817]

Lance,

For the most part, snails wont munch regularly on the plants. It does happen though, especially when thats the only food around. Some types of snails can take over a system very fast! Especially if the water is warm they multiply like crazy! That being said, I keep snails in all of my fish tanks ( for substrate maintenance, clean up crews ETC) and when I build my AP system I will have trumpet snails in there as well... If you are worried about the snails or if there is just way to many, check with your Local FIsh Store on some "Assassin Snails" (Clea Helena) they are only a few bucks 2 or three of them after a week or so to settle in will knock out those pest snail, they reproduce much slower than the pest snails, are slow growers and the few that you put in there will be around to take care of the leftover here and there pest snails in the system.

Parker

[Lance_Green]

Thanks bsfman, bcotton and parker817.

I read Sylvia Bernstein's book, "Aquaponic Gardening". She says grow beds should be 12 inches deep. If the grow beds are 4" and 6" deep, do you think the grow beds will be much less efficient? If so how much less efficient?

Also the grow beds are sloped, maybe 4 inches in 18 feet. Are most grow beds flat or sloped?

Thanks,

Lance

[keith_r]

i like deeper gb's, but shallow will work for shallow rooted plants like lettuce,,, just not very well for things like tomato plants
deeper growbeds provide more filtration in the same footprint..
my gb's are 18-22" deep

[Lance_Green]

Keith,

Thanks for the feedback.

Lance