I did firstly the SAPI but it I found it hard to get aa good reading below 10ppm.. I found
this. It is a little expensive but precise and easy to get an exact reding in after only a few minutes. No color chart.
if you have any other questions about dosing fertilizers let me know.
I have had a lot of algae issues over the years but it was never caused by too much phosphate or nitrates.. But I did have algae when I had low phosphates. But most of the time it was caused by deficiencies, low levels, of any one of the 14 nutrients plants need. In high tech aquarium some people dose 10ppm or more a week and don't have algae issues. Basically in aquariums if you had a nutrient deficiency Algae does very well and your plants won't grow. But when you have no nutrient deficiency plants grow but algae struggles. No one knows why.
If you have high nitrates and phosphates + source of light = you will have algae bloom.
You can't cheat death, taxes and algae bloom in above conditions.
You might test water and it will show low phosphates. That's only because algae will try and gobble up as much Nitrates and Phosphates as it possibly can and store it in cells for later.
But the reason for algae bloom in the first place is abundance of nitrates and phosphates available to it, allowing it to bloom. (same goes for cyanobacteria)
It is the same with low nitrate or phosphate reading in heavily planted tank. The reason test shows low nitrates, etc isn't because there is little nitrates produced in the environment. Low reading is because plants are using a lot of the nitrates the tank produces thus appearing as low on the test.
I've also seen a lot of videos where people draw wrong conclusions from the readings about deficiencies about algae, etc, etc. due to lack of base knowledge on biological processes plants do and counter intuitive effects.
When thinking about plants one has to start at basic truths and draw conclusions from there.
All plants, from algae to lawn grass to trees use 1 of the 2 competing strategies:
1. Fast growing:
will try to out-compete by gobbling up as much resources as it can and grow as fast as it can.
Will often compensate for nutrient deficiencies by making poorer quality leaves, steams, try to grow even taller or faster to reach light/nutrients. Will store excess nutrients.
Lives fast and dies fast once abundance of nutrients is exhausted. (most algae belongs to this category, fast growing steam and floating plants, weeds, etc)
2. Slow growing:
Will try to out-compete by outlasting the fast growers. It will not compensate on structure and quality/health of leaves, steams, etc when faced with nutrient deficiency. It will store some nutrients and slow down growth rate in order to accumulate missing nutrients. If it has good balance of nutrients it will grow as fast as it can without compromising it's structure.
It will grow slow and it will be capable of surviving for long time when faced with lack of nutrients, access to light, etc. Long after fast growers have died down.
Your Anubias and Java Fern belong to this category.
I have Anubias and Java Fern and did few months of experiments on Nitrate uptake, etc (there is a thread on it, albeit derailed and unfinished due to, well internet forum).
If you only have Anubias and Java fern = you will have excess nitrates and phosphates (depending on the food you're adding) without dosing supplements..
If you dose Potassium and trace elements = plants will out-compete algae for nitrates and phosphates and you will have undetectable nitrate levels (depending on number of plants and stocking of course. Java Fern is pretty good at sucking up nitrates) and thus low algae growth.
I have to dose 14ppm Potassium, 1 ppm phosphates and 1mm trace elements every week to achieve 0 nitrate reading and almost no algae. (your system might require different dosage.
If you don't want to dose fertilizers:
Get fast growing plants to out-compete algae/cyano for nutrients as those plants will also compensate for nutrient deficiency while absorbing abundant nutrients, just like algae does.
GL