Nitrates out of control in low-tech tank...is it the Osmocote? - The Planted Tank Forum
 
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post #1 of 10 (permalink) Old 08-15-2011, 01:05 AM Thread Starter
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Nitrates out of control in low-tech tank...is it the Osmocote?

I set up a 55g low-tech tank in April. It was really a complete re-do of an existing tank because I moved. Heavilly planted with ferns, crypts, and a sword. 1.75 wpg of T8s.

I put in some Osmocote, about 50% of the bottom covered one granual deep, toped with about an inch to an inch and a half of Vermiculite, capped with 2 to 3 inches of pool filter sand.

Half the crypts melted to death and never came back...but half are still there and chugging along, not as great as I might have hoped, but surviving.

Originally I was running two bottles of DIY CO2 but gave up after awhile...when I got busy this summer.

Kinda neglected the tank over the summer, house is not air conditioned. Lost some fish (Florida Flag Fish) which I attributed to the tank getting into the low 80s daily for about a month.

Put in some new tiger barbs since they take heat better, but they're dying too. So i tested the water. Nitrates off the charts.

Did some water changes. 75% to start, then two 50%. Also cleaned both cannisters, figuring they are kinda nitrate factories, and this might slow them down.

Nitrates are still off the charts. Tiger Barbs still dying. SAEs seem completely unaffected either by heat, now past, or nitrates. No algae problems either.

I'm going to continue water changes I guess, but, now here's the question. I've not disturbed the substrate since setting the tank up, but as it's just over 4 months I'm wondering about the Osmocote. I assumed as it released it's stuff the Vermiculite would bind up what wasn't being used by the tank and make it available to sword and crypts. Is it possible that the Osmocote, now completely dissolved, is being released by the vermiculite, or just not bound and that there's a very large supply of fertilizer seeping out the substrate that I'll never stop?

Thanks
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post #2 of 10 (permalink) Old 08-15-2011, 01:13 AM Thread Starter
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I should add that I tested the water out of the tap to check that, and my test, and it did not show abnormal nitrates.
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post #3 of 10 (permalink) Old 08-15-2011, 02:44 AM
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yep I would say too much osmocote, remember seeing another thread on here and the op numbers were off the charts after puting an entire bottom layer of osmocote

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post #4 of 10 (permalink) Old 08-15-2011, 03:06 AM
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Overstocked would know more about these membrane type fertilizers than probably anyone else, but I don't believe the nitrogen in osmocote can last that long before being depleted. Some products like Multicote have thicker membranes and can probably last longer, but Osmocote claims to last up to 4 months (which probably means 2 ) when used terrestrialy. I would have to believe that when totally saturated it would deplete much faster.

I may be wrong on this.

I started my grow out tank with probably 4X that much Multicote, but it was brightly lit and CO2 injected, so maybe the nitrogen just got used up faster.

Don't make the mistake of believing that all of that fertilizer stays in the substrate. No matter how you try to cap it, it will still diffuse out into the water column over time.
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post #5 of 10 (permalink) Old 08-15-2011, 04:18 PM
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The rate that Osmocote dissolves is governed by the temperature of the subtrate. That being said I am pretty sure that after 4 months it has dissolved.

http://www.scotts.com/smg/products/o...uct%20Page.pdf

Quote:
Originally Posted by Sharkfood View Post
Overstocked would know more about these membrane type fertilizers than probably anyone else, but I don't believe the nitrogen in osmocote can last that long before being depleted. Some products like Multicote have thicker membranes and can probably last longer, but Osmocote claims to last up to 4 months (which probably means 2 ) when used terrestrialy. I would have to believe that when totally saturated it would deplete much faster.

I may be wrong on this.

I started my grow out tank with probably 4X that much Multicote, but it was brightly lit and CO2 injected, so maybe the nitrogen just got used up faster.

Don't make the mistake of believing that all of that fertilizer stays in the substrate. No matter how you try to cap it, it will still diffuse out into the water column over time.
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post #6 of 10 (permalink) Old 08-16-2011, 12:06 AM
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Yes. Probably. My nitrates hovers at 50 when using osmocote.
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post #7 of 10 (permalink) Old 08-16-2011, 12:09 AM
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Quote:
Originally Posted by Sharkfood View Post
Overstocked would know more about these membrane type fertilizers than probably anyone else, but I don't believe the nitrogen in osmocote can last that long before being depleted. Some products like Multicote have thicker membranes and can probably last longer, but Osmocote claims to last up to 4 months (which probably means 2 ) when used terrestrialy. I would have to believe that when totally saturated it would deplete much faster.

I may be wrong on this.
The difference is an aquarium is a closed system- that nitrogen has no where to go other than plant uptake and water changes. Nitrate dissolved into the water is going to STAY in the water- it can't evaporate and won't run off like it would in a garden or a flower pot.





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post #8 of 10 (permalink) Old 08-16-2011, 12:24 AM
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Quote:
Originally Posted by farrenator View Post
The rate that Osmocote dissolves is governed by the temperature of the subtrate. That being said I am pretty sure that after 4 months it has dissolved.

http://www.scotts.com/smg/products/o...uct%20Page.pdf
Well, yes and no. Osmocote's membrane is thin and designed for use in soil. Cooler temps would make it release slower(the poors get smaller) but in an aquarium, where the temp is above 60 degrees all the time, the temp isn't really relative--and here is why: Since osmocote is designed to be used in soil, they aren't intended to be fully submersed.

This is a LOT of osmocote. 1/4 or 1/8th this much would have been better. I'd imagine there is still ammonia/nitrogen trapped in the substrate and since this is an otherwise low tech tank, the nitrogen/ammonia is not getting used up very quickly.


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Originally Posted by lauraleellbp View Post
The difference is an aquarium is a closed system- that nitrogen has no where to go other than plant uptake and water changes. Nitrate dissolved into the water is going to STAY in the water- it can't evaporate and won't run off like it would in a garden or a flower pot.
This.

I would honestly do a 90% water change(leave enough for the fish to float...) and repeat the test immediately then at 1 hour and then in 12 hours. This is a pretty good way for us to diagnose the issue.

These membrane ferts work pretty well, but some caution has to be taken. You've got a lot of ferts.

The vermiculite doesn't float? That seams like a LOT of vermiculite and I'm not sure how beneficial it is.

If it were me, I'd take everything down, put an inch or so of top soil, a dusting of osmocote, and cover with sand.
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post #9 of 10 (permalink) Old 08-17-2011, 03:02 AM Thread Starter
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The vermiculite doesn't float. I soak it before using (soaked for a month actually). I don't go digging in the substrate, so it stays under the sand. The vermiculite that did get to the surface during setup, and some minor tweaking i had to do along the way, is certainly "light" but does settle on the bottom in the nooks and crannies, breezes will push it around. It is, however, very easy to clean up with a gentle vacuuming. I started the co2 back up, can see new algae after a day as a way to use up nutrients...

Will try the big water change and testing tomorrow. Thanks for the idea.
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post #10 of 10 (permalink) Old 08-20-2011, 02:11 AM Thread Starter
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Before water change: 80 mg/l +
Water in: 0 mg/l
After 80% water change (only 80, forgot about water in filters): 15 mg/l
One hour later: A little over 20 mg/l believe.
8 hours later: 40-80 mg/l
20 hours after water change: still looks like 40-80 mg/l...the two colors are hard to tell apart.
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