Hi,

I have a heavily planted 50 gallon tank. Plants are amazon, melon and pigmy chain swords, apogenton, cardamine and dwarf sag. I use a lot of CO2, around 30ppm. Everything grows like crazy and I am happy but I have no idea how much potassium I should add as I don't have a test kit. I measure nitrates and phosphates and they are fine and I don't need to add any as fish food is enough. I just add micronutrients every maybe 2 weeks, 1/4 tspn of CSM+B which comes to around 0.5ppm of iron in my tank.

I add 1 tspn of K2SO4 once every two weeks as an insurance but I don't really know if that is enough, that should add 15ppm of potassium in my tank.

I don't change the water at all so I can't do estimative indexing.

The only thing not performing 100% is apogenton, middle of the leaf becomes black and the leafs are constantly dying but the new ones are emerging all the time. I am not sure if this is normal or it indicates potassium deficiency. Everything else does not show any symptoms like holes in the leafs or something like that.

As a side story I tried to disconnect the CO2, after about a month everything started dying and the water was not clear any more. I wanted to have less maintenance with trimming but it seems that the plants are either thriving or dying.

Thanks,
David Zaninovic

IMO if you are running a tank with CO2 and are adding nutrients such as CSM and K then doing some periodic water changes, even if not every week, is a great help in reducing excess accumulation and/or deficiencies of particular nutrients. Even if you are not following a strict EI regime adding a bit more K than you think you need and then changing water every so often to make sure you don't end up with too much will save you some stress, money on test kits etc. I guess the amount you add is enough but others will probably be able to give a more accurate answer in that respect.

cheers
Neil

I measure iron levels before adding CSM+B to make sure I don't go over 0.5ppm. I change some water when I change the filter, 2.5 gallons maybe every two weeks. I did few 90% water changes in the past maybe 3 months apart. I know it is not supposed to be healthy for the fish but nobody died and I have a farlowella inside. Nitrates are at 10ppm in the evening and they go up to 20ppm in the morning. I think it would be best to get that $30 potassium test kit.