dosing iron and phosphate - The Planted Tank Forum
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post #1 of 5 (permalink) Old 09-14-2018, 09:17 PM Thread Starter
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dosing iron and phosphate

Read this on another thread and decided to not take over the original poster's thread and make a new one.

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Originally Posted by Seattle_Aquarist View Post
Hi @The Algae Farm,

Welcome to TPT!

Yes, based upon our discussions @Cyano is dosing macros two days a week and micros on different days two days a week. I believe the two nutrients that you are referring to are iron (in the CSM+B) and phosphate (in the KH2PO4) which if dosed at the same time will form iron phosphate and be unavailable to plants. It stands to reason if we make iron and phosphate unavailable to our plants then growth is likely to be affected.
I've read about not dosing kh2po4 and csm+b at the same time but I always thought it referred to people who dump the dry ferts in their tank. I think I read somewhere that doing that the precipitate will not dissolve.

I mix my dry ferts in a jar (kno3 and the kh2po4) together dump it in the tank then mix the csm+b in a jar and dump it in the tank. Both jars are fully dissolved.

Should I not do that?

Very curious to know. Thanks
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post #2 of 5 (permalink) Old 09-14-2018, 09:59 PM
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Hi Frank158,

My Mom went to college in Winnipeg; she was a chemistry major!

No, you should not do that. When the KH2PO4 is added to water it forms phosphoric acid and potassium hydroxide. If there is any phosphoric acid (H2PO4-) still in solution when the CSM+B is added then the ferric (Fe2+) ions in the ETDA chelated iron will bond with the phosphate to form FePO4.

CSM+B is not the best source of iron for many aquariums. If there is an abundance of calcium in water the iron will readily bond with the calcium molecules. At low pH levels (i.e. 6.0) the iron in CSM+B is readily available to plants however it drops off rapidly such that at a pH 6.5 only 50% of the iron is available and at pH 7.5 only 2.5% is available to plants. Most of my planted tanks are acidic but I have one that tends to be about [email protected] In all of my tanks I dose about half my iron as CSM+B (mostly for the other micronutrients) and half my iron as ferrous gluconate (as found in Seachem Flourish Iron).

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post #3 of 5 (permalink) Old 09-14-2018, 10:06 PM Thread Starter
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That is so cool about your Mom going to school here.

Okay I think I understood what you wrote but have one follow up question. Does waiting 24 hr to dose the CMS+B remedy all that in regards to iron? Or should I still supplement with the Seachem Iron?

How much would you say I should dose the Seachem Iron in a 200L tank. Medium lighting/EI dosing and CO2 is added.

Cheers

edit: forgot to mention substrate is seachem flourite black sand, if that make a difference to the iron
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post #4 of 5 (permalink) Old 09-14-2018, 10:23 PM
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Hi @Frank158,

After 24 hours the phosphoric acid will have 'broken down' and bonded with other positive cations in the water so there will be none of the iron to bond onto. The issue with pH and iron availability of EDTA chelated iron (like in CSM+B) does not change however.

I tend to dose my iron higher than some (no shrimp tanks) but not as high as others with 0.7 ppm added weekly (or 0.35 2X per week). I have measured the water volume in my tanks with about 2" of substrate I find my actual water volume is about 20% lower than the stated "tank size". In that case a 200 liter aquarium would have a water volume of about 160 liters, dosing Seachem Flourish Iron to reach 0.7 ppm of Fe would require 11 ml (about 2 teaspoons) in that tank.

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post #5 of 5 (permalink) Old 09-14-2018, 11:00 PM Thread Starter
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@Seattle_Aquarist

Thanks!
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