Fighting algae with more phosphate

The newly planted vallis seemed to be doing poorly with the leaves suffering structural damage and since vallis is thought to be sensitive to damage from liquid carbon I stopped the daily dosing of EasyCarbo.  Stopping the daily liquid carbon is something I had been thinking about doing anyway, on the grounds that with injected CO₂ gas the “carbon” part definitely wasn’t needed and I was never really sure whether the daily low dose EasyCarbo (1 ml / 40 L) was suppressing green spot algae at all.  That said, I did notice what seems to be increased aggressiveness on the part of the algae in the weeks after stopping the daily liquid carbon.  What do to?  I would like to give the vallis a fighting chance to get established…

Low phosphate does not prevent algae

Despite a lot of misinformation in the popular literature, reducing phosphate is not a way to control algae, in fact, the low phosphate will adversely affect the plants in the aquarium reducing competition for algae.  In any event, with estimative index fertilisation, none of the major fertiliser components, including phosphate, are ever limiting and it’s well established that “excess” fertilizers do not promote algal growth in aquaria.

Can high phosphate prevent algae?

There are some tantalising anecdotal reports that high phosphate can prevent algae.  I have been dosing weekly phosphate to 3 ppm, but I’m going to give 7 ppm a try and see if that has any kind of noticeable effect.  Since it was time to mix up a fresh batch of macro fertilisers, it was very straightforward to boost the phosphates by adding just a little more KH₂PO₄.  My current macro mix is made up to a total of 500 ml and dosed 10 ml per day on Saturday, Monday, Wednesday into a 40 L water volume tank.

Overall, this works out to 25.3 ppm K, 6.9 ppm PO₄, 15.2 ppm NO₃, 4.9 ppm Mg plus whatever is in the tap water used for water changes, which also probably contributes a few more ppm phosphate.

Happy with higher phosphate

It’s been more than a year now since I increased phosphate to 7 ppm per week and happily, in all that time I have not had to scrape down the walls of the Fireplace Aquarium to remove green spot algae.  I can’t say for sure it is the increased phosphate that has made the difference, but before increasing phosphate the tank needed an algae scrapedown on a roughly monthly basis.  Interestingly, I do get green spot algae growth in the water condensation on the lid of the tank, but not in the water column which supports the idea that something about the content of the water column is the difference maker there.

I have made 7 ppm weekly phosphate part of my permanent estimative index fertiliser strategy.