Evaporation?

[Bill Moore]

One of the more surprising revelations of my first winter with my "Plan B" aquaponics set up in the basement is the amount of evaporation taking place in the system. I haven't yet measured the humidity level in the basement, but it doesn't seem overly damp.  Could be co-locating in the furnace room is part of it and it's been an unusually warm and dry winter here on the northern plans. I am having to add as much as 4 gallons of new water every couple days.  

I plan to buy a humidity gauge to measure levels in the basement.  I just want issues with mold developing.  I run a small fan on the floor next to the sump and fish tanks to prevent any damp spots from developing.

[Darrin Charbonneau]

Hi Bill,
I would have mold concerns with that much humidity in.any house. It might not show up immediately, but it will. I have a similar set up in my garage. Even with venting and leaving a window open it still gets everything moist. Enough to swell plywood! Is there a way you could enclose your system and add a exhaut fan to the outside? Black mold is dangerous. Kinda defeats the purpose of growing healthy food. Keeping the temp dow will help, tilapia seem fine @ around 74'.

[Bill Moore]

Thanks Darrin.  Thinking I may keep the indoor system with the goldfish for winter so I can keep water temperature around 70F and put the larger system with tilapia out-of-doors.  That will require, however, running power outside. $$$.  :-)

[Jon Parr]

The evaporation I can handle, it's the condensation that bothers me. The morning after a cold night it looks like a sprinkler was running all night.  Any surface that causes condensation absorbs the heat of evaporation, and this absorbs the heat that was meant for the fish and the plants. I plan to increase the airflow in my room, and duct the incoming and outgoing air through a heat exchanger. No doubt the humid outgoing air would condense against the cold air inlet, passing on at least some of it's heat, and the condensate could be diverted back to the fish tank, so long as the exchanger wasn't toxic. I'm thinking 20' of 6" metal furnace ducting for outflow, inside an insulated 10-12" inflow. 

[TCLynx]

Add a cover over the fish tank and do it in manner that still allows some air to the tank but so that the water condensing on the lid of the fish tank will drip back down into the fish tank, This should have some effect.

[Jeremy Wheaton]

Hi tc, what kind of plastic is appropriate for a tank cover? I have some black contractor plastic sheeting, but it smells very "plasticky" and makes me think that I wouldn't want condensation from that surface to drip back into the tank. I have an indoor setup with a 100 g stock tank attached to a 275 g tote, so I lose quite a bit to evaporation and would like to minimize it if possible. Thanks for any tips!

TCLynx said:

Add a cover over the fish tank and do it in manner that still allows some air to the tank but so that the water condensing on the lid of the fish tank will drip back down into the fish tank, This should have some effect.

[Matt T.]

Jon. Watch out if you use metal. Especially galvanized. Not good for fish/plants. Maybe plastic duct would be better?

Jon Parr said:

The evaporation I can handle, it's the condensation that bothers me. The morning after a cold night it looks like a sprinkler was running all night.  Any surface that causes condensation absorbs the heat of evaporation, and this absorbs the heat that was meant for the fish and the plants. I plan to increase the airflow in my room, and duct the incoming and outgoing air through a heat exchanger. No doubt the humid outgoing air would condense against the cold air inlet, passing on at least some of it's heat, and the condensate could be diverted back to the fish tank, so long as the exchanger wasn't toxic. I'm thinking 20' of 6" metal furnace ducting for outflow, inside an insulated 10-12" inflow. 

[Matt T.]

I use 3/4 pink foan insulation panels on my tank. Nothings died yet, and it helps keep the heat in to. I would keep the fan for the plants to strengthen them, and keep the powdery mildew away. Otherwise the fan will just cause more evaporation if its directed at the FT or sump. The deep water raft people use blue foam board for leafy greens, as the red spectrum would cause them to bolt. As long as the pink is just covering the FT it shouldn't be an issue for the plants.

Jeremy Wheaton said:

Hi tc, what kind of plastic is appropriate for a tank cover? I have some black contractor plastic sheeting, but it smells very "plasticky" and makes me think that I wouldn't want condensation from that surface to drip back into the tank. I have an indoor setup with a 100 g stock tank attached to a 275 g tote, so I lose quite a bit to evaporation and would like to minimize it if possible. Thanks for any tips!

TCLynx said:

Add a cover over the fish tank and do it in manner that still allows some air to the tank but so that the water condensing on the lid of the fish tank will drip back down into the fish tank, This should have some effect.

[TCLynx]

Some of the "pink" foam my have chemicals in it that could be less than good in the system but I'm not sure I've seen any proof that those chemicals leach from the boards.  The Dow Blue Board is the accepted type of foam for commercial raft culture.  1/2" or 3/4" dow blue board is also readily available at lowes or home depot around here so that might be a good material to make a tank cover from. However since it is insulating you might not have as easy a time getting the condensation to form on it and drip back into the tank from it.

Polyethylene would probably be the preferred type of plastic in my book for a condensation cover but it will be harder to support over the tank in such a way that the water will drip into the tank rather than out of the tank.  Remember to leave some air space to make sure your tank doesn't suffocate.

Most of my tanks are outdoors so I'm not worrying much about evaporation since it isn't like it will cause my house to be too humid and cause mold.  So most of my tank lids are simply made with fence panels and netting.  I have made some with non pressure treated wood before, painted with glossy exterior latex paint.  I have used pond liner as a cover over a support of sorts before as well.

Get creative and just make sure to build it to be easy for you to access the fish tank.  I like to have a support or a string that I can swing the cover up and hook it to while I'm accessing the tank and then I can let the cover back down when done. 

[Jeremy Wheaton]

Thanks for the reply, I'll see what I can come up with based on your suggestions. Have a great day.

TCLynx said:

Some of the "pink" foam my have chemicals in it that could be less than good in the system but I'm not sure I've seen any proof that those chemicals leach from the boards.  The Dow Blue Board is the accepted type of foam for commercial raft culture.  1/2" or 3/4" dow blue board is also readily available at lowes or home depot around here so that might be a good material to make a tank cover from. However since it is insulating you might not have as easy a time getting the condensation to form on it and drip back into the tank from it.

Polyethylene would probably be the preferred type of plastic in my book for a condensation cover but it will be harder to support over the tank in such a way that the water will drip into the tank rather than out of the tank.  Remember to leave some air space to make sure your tank doesn't suffocate.

Most of my tanks are outdoors so I'm not worrying much about evaporation since it isn't like it will cause my house to be too humid and cause mold.  So most of my tank lids are simply made with fence panels and netting.  I have made some with non pressure treated wood before, painted with glossy exterior latex paint.  I have used pond liner as a cover over a support of sorts before as well.

Get creative and just make sure to build it to be easy for you to access the fish tank.  I like to have a support or a string that I can swing the cover up and hook it to while I'm accessing the tank and then I can let the cover back down when done.