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Old 02-06-2007, 08:30 PM   #76
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What happens to the agar when it dissolves in water? Is it pretty much inert, or will it turn our tank water into something bad and smelly?

I assume the image with the agar in the substrate serves to illustrate your point... to evenly dose the tank this would have to be put in an area of current, maybe into your filter.

And the prize question: How long does it take to dissolve a (smallish) cube of agar in water?
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Old 02-06-2007, 09:43 PM   #77
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Agar will not dissolve in water unless you boil it (just like gelatin). It will likely eventually decompose if buried in the substrate. If you kept it on top, you could easily remove it.
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Old 02-06-2007, 11:17 PM   #78
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Quote:
Originally Posted by defdac View Post
You know this for a fact?

What about this then?
Damn, I got moded! Okay, my bad. I admit, all I know about agar is that kanten is delicious and they use it in petri dishes. So how come it doesn't grow fungus or bacteria in the substrate? When culturing plants in agar, I know you have to take great measures to keep everything sterile.

Anyway... if it doesn't dissolve in water, but will decompose slowly, can you include enough salt (and still solidify the agar) to make this a viable dosing option, or is it used just as growing medium?
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Old 02-07-2007, 06:09 AM   #79
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Yes it was very persistent in the substrate.. It remained in shape for more than 6 months and then slowly began turn to mush (decompose), so I guess it's mostly for growing medium.

I had hoped someone would say it would dissolve, but just very very slow. A bit of searching seems that Kelley is right. It will not dissolve until it reaches 100 degrees.

Oh well *shrug*

I think this thread have raised many good points and I will definitely try some of this dry-dissolving out if it seems to work! Thanks all and especially Wasserpest.
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Old 02-07-2007, 03:37 PM   #80
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It was a good idea... if anyone finds a slowly dissolving, inert substance that can be mixed up with salts... please share. Jello?

That would deserve its own thread.
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Old 02-07-2007, 05:17 PM   #81
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Salts will freely diffuse out of the agar. Larger molecules will as well, though at a slower rate. Once the agar sets, it creates a porous network. This feature is exploited in the use of agarose gels used to analyze DNA fragments by size. Agarose is just highly purified agar that is used by molecular biologists.

These agar-fert blocks might work, but I would like to offer a few suggestions. First, be sure to sterlize your casting tray of choice. (Maybe use an ice-cube tray?). You could do this the way that home-canners sterilize jars by using a boiling water bath or the dishwasher. Boil the solution thouroughly. This is needed to dissolve the agar and keep things sterile. This may not be a good idea for traces because the heat might dissrupt some of the chelation of the traces. If I were in the lab, I would simply pass the trace solution through a 3 micron filter to sterilize it and add it directly to the agar once it had cooled to a reasonable temperature. (~65 degrees C is good. cool enough to handle.) This is the method that I use to add antibiotics and drugs to the agar media that I make. Second, I would do some bottle tests to check the diffusion rate of the ferts from the agar blocks into the water column.

So, in summary, this could work as a way to make dosing blocks for at the very least macros. You could put a small sterilzed stainless steal washer in each block to help it sink. I can't tell you how long a block would last, though.

Oh, and i would not use jello. Agar is a polysaccharide, whereas gelatin is a protein. You do not want decomposing proteins in your tank! Your poor fishies!
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Old 02-07-2007, 06:35 PM   #82
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I still dont understand why you have to sterilize everything, but then you can drop it in your tank and it's okay. Is it only vunerable in liquid form?
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Old 02-07-2007, 07:29 PM   #83
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You need to be sterile if you want to make more than one at a time. I would assume that you would for time-savings. Otherwise, it would be a lot simpler to dose your tank some other way. You would be surprised the nastiness that will grow on this stuff! These should be kept refrigerated, as well.
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Old 02-07-2007, 07:48 PM   #84
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Kelley, thanks for your advice!

One big problem with using agar-like substances that do not dissolve is that the rate of fertilizer dosing will change over time. Initially, a fresh block will provide a very high concentration of nutrients diffusing into the water. As it gets exhausted, less and less fertilizer is going into the water.

I want an absolutely linear dosing. Using a tube containing the fertilizer will provide that, more or less, since the surface of the exposed fertilizer doesn't change over time.
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Old 02-07-2007, 08:25 PM   #85
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Wasserpest, you are correct that this will not provide linear dosing. It also sounds like a messy, fussy business. My kitchen is messy enough!
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Old 02-07-2007, 10:21 PM   #86
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What about using the upside down test tubes with a rubber stopper and glass pipe running through the stopper toward the top (actually the bottom) of the test tube. By varying the length of the glass pipe you would vary the concentration that was exposed to the tank water. This may run into the same problem with the biofilm but, I think the tube might be large enough to avoid that problem.

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Old 02-08-2007, 06:10 PM   #87
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My guess is that this will not dissolve fast enough. If I understand you right, the glass pipe would run through the fertilizer and stick out on the top? I think there would not be enough flow in there to dissolve the salts. Plus, as the level of the salt goes down, distance between the top of the glass pipe and the fertilizer increases, and less fertilizer would be dosed (I imagine).
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Old 03-19-2007, 12:56 PM   #88
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Depending on how automated you want to go I have found that a simple IV bag or gastronasal feeding bag for babies works well. I mix 1 weeks worth of ferts in 2L of dechlorinated water and fill the bag. I have adjusted the drip rate so that by day 6 or 7 the bag is empty. Takes 10mins or less to setup on a sunday nite and then you are free all week to enjoy the tank.

As a side note when you go to the drug store to ask for a the bag ask for the gastronasal one you get very strange looks if you ask for an IV bag. They are essentially the same thing except one has a needle fitted to the end which you do not need anyway.
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Old 03-19-2007, 04:34 PM   #89
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There are two issues with the IV bags... 1) Difficult to hide and 2) settling of solutions. They are also susceptible to solutions degrading over time...

Especially 1) makes it a non-starter for me. It would work good if you had a sump and some room above it in your stand.
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Old 05-30-2007, 04:05 PM   #90
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It's been a couple of months, and "Test tube dosing" supplies phosphates to all my tanks now. KH2PO4 dissolves fast enough to not need a lot of water flow, and it is easy enough to find a little plastic tube either left open, or reduced with a stopper with a hole in it for smaller tanks.

I don't really test for phosphates. I know my water doesn't have any, and my plants don't need a whole lot, so I start with say 1/4 tsp and figure it should be enough for 4 weeks, make a note when I add it to the tank, then just watch.

You can see one in action in my 100gal tank here: http://www.plantedtank.net/forums/ph...tml#post422296

Neat thing is since P doesn't mix with micros (iron), you could dose P this way and the rest of the ferts mixed together with another application of your choice, peristaltic pump, water pump, air pump, whatever.
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