High iron dosage and odd precipatate in tank
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)
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!