# Dosing with Eheim Auto-feeder experiment



## trashion (Jan 6, 2008)

Cross-posted to www.fishforums.com and www.aquariacentral.com.

So I picked up an Eheim auto-feeder a while back, and I'd read some threads about using it to dose dry powdered fertilizers on aquaticplantcentral.com.

The posts were inconclusive, though one person said he'd been doing it for years. Well, that was my cue.









Here's the box!

First, I googled the capacity of the container. Someone said it held 100 mL. As I didn't know, you can't really convert ml to grams without knowing specific density et al. Several sources said just assume 1g=1ml. So I did that.

I've been using the Estimative Index method to dose macro ferts. It worked pretty well, my plants were growing quite fast.

Using the 1g assumption, I calculated how much of each fert I would need. I use the 10-20 formula on the EI site, so that's 1/32 tsp of K2SO4 and KH2PO4 and 1/8 tsp of KNO3. Math is NOT my thing at all, so I got frustrated. But I figured it out.

I happen to have a handy-dandy gram scale for measuring dietary supplements, so I whipped that out. I figured out that I would need a 3:1:1 ratio, or 60 grams of KNO3, 20 grams of K2SO4, and 20g of KH2PO4.








Calculations! 

I measured these out in my fishfood lid on the scale, and loaded up the feeder.








Turns out 100 grams only fills it up about halfway, but oh well!

Now where to position it? The packaging recommended on the back of the glass top behind the light, but the feeder's too big to fit there. My friend pointed out that if I put it on top of the light, it would dump the ferts directly into the outflow of the filter! 








Smart kid! I was worried about heat from the light, but it only gets warm, not hot, on top.

So I positioned it, opened it to what I thought was a very small dispensing size, and pressed the Eheim button to make it dump the ferts in. Oops. Should have tested it outside the tank! It dumped a TON of fertilizer in.

Here's the feeder drum after it dumped a ton into the tank:








Yeah, it was a lot. It was half-full before that!

Waterchange time!

No pics of that, as I was a little bit frantic trying to get all the fertilizer out of the tank. Using the scale, I calculated out that it should dump ~.75 to 1 gram of ferts daily. So I played around with setting the opening of the autofeeder to the smallest little crevice, until it only dropped about .8 grams. Not bad at all.








There it is!

A few things:
1. These ferts have different densities, and to get a uniform mixture in the feeder, I'd probably have solublize them, boil them down, and get a uniform particle size. Or something. That's what someone on APC said, I'm terrible at chemistry. I have no way to measure how much of each fert gets into the tank, but from what I've read, the amounts don't really need to be exact, and if there's more phosphate one day and less nitrate the next, it really won't make much of a difference in the long run. 
I've got a mean algae-scrubbing muscle in my right arm 

2. The powder definitely gets into the mechanism if you're not careful. I think every few weeks, I'll take it apart and blow out all of the powder. Otherwise, it can burn the feeder and stop it from working. Short-term solution, don't tip the feeder the wrong way. I might try to put some teflon tape over the connection between the feeder mechanism and the drum, so air can still get through(there's a little fan inside to keep the ferts from clumping.

Pros:
-I won't have to measure out and dose dry ferts daily.
-Ego boost from figuring this out!

Cons:
-Can't set it to dose every other day. So I'm going to try and get it to the tiniest notch possible..perhaps I'll even seal the drum and drill a tiny hole in it, so that it will dose smaller amounts daily.
-Still gotta dose flourish every other day, but hey, that's not so hard.

Hope you enjoyed my writeup, I'll be rushing to my room between classes at 12:10 tomorrow to make sure it doesn't dump too much in!

Comments and feedback greatly appreciated!


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## MartialTheory (Dec 20, 2007)

cool. Let us know how it works in the following days. I always heard auto feeders are bad as a fert dispenser but lets see how this one works.


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## trashion (Jan 6, 2008)

Yeah, I was concerned about moisture, but I think I might be able to pull it off with this one, the drum of ferts is far away from any water, and there's an internal fan to keep it dry.


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## trashion (Jan 6, 2008)

Update: I woke up this morning to a cloudy green tank, and dead shrimp 

It would appear that my waterchange after dumping in too much fertilizer did not do enough, as my nitrates tested off the charts (at least 180!) Fortunately, all 12 aspidoras and 5 harlequins are fine.

I've been changing water in between classes, and I got the NO3 down to about 50, but i'm still water-changing :\ This project is going on be put on hiatus for a few days, as I'm going home this weekend. More updates next week.


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