Water changes in low tec tank

[laka]

My tank has been set up for 3/52 now. Evrything appears to be OK. One problem i had is my angelfish breathing at the surface. One died. I added a small powerhead to agitate the water and this seems to do the trick. I top up with water from evap. loss. I dose accordingly. I need to add 5g KNO3 every 10 days in the 180g tank to keep levels at 6ppm. PO4 0.5ppm GH KH 4-5 degrees. pH 6.9 in morning and 7.5 after light out. By the way my plants a pearling like crazy with my metal halides on (2wpg)-and no water changes.
I am noticing a fine matt of algae on the glass. Is this normal?
Now to my questiom. Tom advised no water changes in this tank set up, which i like.
My concern as i was alluded to in another site is that this will inevitably lead to a rise in TDS heavy metals hormones and DOC's and other "unknown metabolites" which may be detrimental to fish health esp. my angelfish that like soft water.
Is this a potential problem? I thought plants can purify the water indefinitely as long as i don't overfeed overfertilize.
Comments please.
LAA

 

[Tom Barr]

My concern as i was alluded to in another site is that this will inevitably lead to a rise in TDS heavy metals hormones and DOC's and other "unknown metabolites" which may be detrimental to fish health esp. my angelfish that like soft water.
Is this a potential problem? I thought plants can purify the water indefinitely as long as i don't overfeed overfertilize.
Comments please.
LAA

What do plants suck up?
Metals, hormones are not bad, DOC's are not bad as long as the loadign rate is slow, which in a balanced non CO2 tank, is the case.

Folks for the last 20+ years have used non cO23 methods w3ithout water changes for years, but generally one every 6 months or so is good, and that's due to a large pruning etc.

Which brings you to the export, the plant assimilation of the nutrients.
The rate of fish waste and in puts are low, thus the fish waste gets sequestered into plant tissue.

If your plants riot and do poorly, that is like adding too many fish, it slows down the removal and adds to the problem.

You should likely clean the glass good make sure there's enough surface movement(this is a non CO2 tank after all), do a tiny water change to remove any algae, get some algae eaters etc.
Add more plants, eg Crypts most spots, Java fern/Anubias in the darker areas etc

Floating plants help some as well.

Tom Barr