High iron dosage and odd precipatate in tank

[greeneggs]

Hi, hope you can help me.

We have a 130 litre 3ft planted tank. Most of the plant load is comprised of crypts, with grasses and stem plants accounting for about 30%.

After having had a regular and apparently successful dosing regimen for 2 and half years, in the last 2 months crypts in particular have developed signs of severe chlorosis. Almost all new growth is coming in bright green, and older leaves are now affected.

I started upping our Flourish Iron dosing from 3ml a day, about 3 weeks ago, adding 2ml extra daily, and testing every night. I am now up to dosing 20-22ml of iron once a day, and still nightly tests show no Iron left in the tank. I've tested the kit and it it's working.

I've also begun adding potassium at 3ml every two days, which I have never dosed previously as a few older leaves were developing holes.

Crypts are starting to show minimal signs of improvement, but in the last few days a pale rusty coloured lint like substance has started to build up, settling on the surfaces of equipment and becoming trapped in grasses. Can you suggest what it is? I'm reluctant to continue this dosage without knowing what this substance might be.

Other water parameters:(Before bi-weekly water change)
Ph: 6.8
Nitrate: 2ppm
Phosphate: 0.5ppm
GH: 6.5 (much higher than usual due to drought conditions)
KH: 4.5 (maintained with Alkaline buffer)
CO2 injected and Excel

Substrate - sand, with laterite and Flourish plant tabs.

Thanks for your help!

[Tech Support GL]

That rusty tint is probably Some of the iron falling out of solution. There is possibly too much iron and it is not staying in solution and you are seeing it covering things in the tank. The chlorosis could be coming from a deficiency in some trace elements. I would suggest trying Flourish trace with your dosing and giving it a little time for improvement. Here is a link to some info on Flourish Trace; http://www.seachem.com/products/product_pages/FlourishTrace.html. The link also has good info on deficiencies and signs of trace element deficiencies.
Seachem Support

[greeneggs]

Hi :)

Thank you very much for your reply - I've been away for most of the last fortnight, which is why I didn't get to thank you straight away.

We've been using Trace twice a week (7ml at each dosing for our 130 litre tank) for almost the entire time of our tank set up. Do you suggest a higher dose?

Is it unusual that we would be getting a test result which shows zero iron left in our water at the end of the day if some iron may have dropped out of solution and have left a residue?

Would dosing at intrevals during the day prevent the iron falling out of solution and allow the plants to masximise their use of the available nutrient?

Thanks for your advice.

[Tech Support GL]

You are welcome for the response. The 7ml of Trace that you are using is according to the dosing for the size tank you have. The iron test could be reading zero because the iron has fallen out of the water and settled. When you test for it in the water it is not there. Try smaller doses of iron to prevent the precipitation and checking the iron to see how quickly the plants are utilizing the iron and adjusting you levels according to plant usage.