Why dry dosing?

Re: Why dry dosing?

not many people would be willing to put money into a pump to do the dosing. and then you would have to have 2 of them anyway since you shouldn't be dosing traces (iron) and PO4 at the same time. so I would say that dry dosing is meant for individual control of what goes in the tank, as you said above.

i am interested however in the pumps you are referring to. can you post some pics of the setup you have?

 

Re: Why dry dosing?

I believe the idea is that the trace chelating agent precipitates some of the macros. There certainly is a precipitate when I mix trace and macros although I’m not exactly sure what it is. Doesn’t matter really; it’s something I want dissolved in the column and it’s not.

 

Re: Why dry dosing?

In high enough concentrations, Fe and PO4 precipitate out as FePO4. Don't ask me what those concentrations have to be for this to happen !

According to Tom, Fe is sometimes used in natural water systems (lakes etc.) to remove PO4 by precipitation...

 

I am dry dosing manually, and would really like to dose PO4 and Fe on the same day (I have a low light tank and am working towards dosing once a week). Can I do this? If so how close can I get away with? hours, minutes even? Will I visibly see the precipitation if I get it wrong or not necessarily?

Also! When doing water changes I add my water conditioner straight into the tank. Will this take out some of my nutrients? I know it is designed to remove nitrates, but what about any others? and should I wait a certain amount of time after dosing that before adding my dry ferts?

Sorry for my flurry of questions today, I did have a search of the forums for a while before posting!

 

BTW As an addendum to my last post I am curious to the science and not just looking for instructions... I wonder if the phosphates need to just dissolve into the water, or whether it has to be used up completely by the plants before adding the iron.

 

A water conditioner, actually a dechlorinator, such as Prime is intended to neutralize the chlorine and ammonia in tap water, not to remove nitrates. If you dissolve phosphates in water, then add chelated iron, you get a cloudy mixture containing a precipitated Iron phosphate compound. If this is done in the aquarium, the precipitate settles on the substrate, where it is eventually available to the plants. But, we want it to be available when we dose it, so we don't want to dose phosphates and iron at the same time.

 

I have a question on the Iron/ PO4 thing. If you have a fancy substrate which are often sold as containing high levels of iron, is there a danger that the huge reservoir of iron locks up all the phosphate you are adding to the tank when dosing?

I will add some figures here, in case it makes any difference. I'm adding 1/16th teaspoon potassium phosphate twice a week to a 22 US gallon tank, 85 litres ish. My tap contains about 0.7 ppm in it's own right (based on test kit.... ) 50% change once a week.

I forget what my substrate was called - AquaPlantoSurge or something similarly silly but it it is a UK plant substrate for aquariums comprising white/black/grey grit stuff which is so iron rich that some bits leap onto the magnetic glass cleaner if it goes too close.

Any thoughts from chem boffins welcome

 

Interesting. I have only recently started using the EI and I still feel the need to comfort myself with the odd test kit. Last week I was adding Phosphate and testing, before, and then after half an hour or so, to see if the dosing calcs were giving me a reasonable concentration.

I noticed that I couldn't detect the great change the fertilizing calcs were suggesting.

I was thinking this could be a) rubbish test kit (imagine) b) poor calcs c) the dry potassium phosphate I was using was odd, or fake, or had some other problem.

Might it be that the PO4 was going straight into the iron rich substrate and thus not appearing in the water column concentration test?

From what you have said Tom, I guess that wouldn't be such a problem since the plants could still get at it via the substrate, so as long as I keep adding it into the tank it'll be fine, regardless of the water column concentration reading?

Suddenly the "throw out your test kits and look at the pesky plants" philosophy starts looking more and more sensible !!

 

Thank you Tom for pointing out the obvious answer - "try it out and see"!

I did the experiment and the PO4 test did not show any darker blue colour than 0.7ppm even when I chucked phosphate in by the handful (well almost). So it has "gone off" in the 6 months since I bought it.

I bought a fresh kit and found my tap water is 2.5ppm, the water in my tank was actually nearer 5ppm...of course it's still only another test kit but hey..

This little practical experiment has confirmed to me two things which I know you have mentioned repeatedly on this site,

Firstly you have to be very suspicious about test kits (especially that they change over time)

Secondly an excess of Phosphate does not automatically cause an algae apocalypse as everyone in every LFS etc maintains. I have been dosing up Phosphates to about 5ppm while reading 0.5-0.75 on the test for a few weeks now. I must be one the few fools who have actually done this heretical thing in their precious aquarium.

I can report that I have a tiny smattering of BBA here and there on the odd leaf, but the tank is looking better than I've ever managed previously, by following your advice about plenty of CO2 and a weekly water change.

Thanks again for the advice