Phosphorous Phear

Well kids, the time has come for us to have the TALK. It's as uncomfortable for us as it is for you, but ignorance is dangerous and we want nothing but the best for you. There's no use beating around the bush any longer. Let's talk about phosphate.

Phosphate has been vilified by aquarium keepers for nearly as long as we've known it was in our tanks. It's been considered algae fuel with no upside and as a result, we've all expended massive amounts of cash on removing it entirely from our aquariums. Honestly, it wasn't until some of us really started getting into planted aquascapes that this mindset shifted at all! In total fairness, there was some merit to our loathing of the compound; when phosphate levels are too high, and out of balance with other nutrients, it IS an algal fuel, and there is nothing like algae to make your plants suffer and any tank look bad.

The truth about phosphorus is a bit more nuanced. As we grow, we learn (or maybe we have that backwards). The point is that over time the science we adhere to reveals both weaknesses and strengths in what we knew before. It turns out that phosphates are not only critical for your plants, which we'll get into later, but also absolutely vital for the health and wellbeing of your fish and invertebrates too.

ATP is an acronym that stands for Adenosine Triphosphate, which is how all biological functions are fueled (notice the phosphate part of that name). Everything from using muscles, to metabolism, to nerve impulses are dependent on phosphorus. Phosphorus is also critical for making and maintaining DNA and RNA, without which your fish and inverts could not reproduce, or heal, or even exist. Calcium phosphate is a primary component of skeletons, teeth and exoskeletons (for inverts). The availability of calcium for your snail shells is directly tied to phosphate (among other elements). Phosphates are a fundamental part of your aquarium's health, and not just as it relates to your plants!

On the topic of your plants, they need it too. Phosphate is essential for plant growth. When you see fertilizers for your garden, you'll always find three numbers on them, for example 5-5-5. These numbers are how much of each compound this fertilizer contains in the format: nitrogen – phosphorus - potassium. So, it's one of the big three. Plants need the same ATP that your fish and inverts do, but in plants it is needed for photosynthesis, growth, respiration as well as basic cell structure. It's also a key element in promoting strong root structures, flowering and general plant vitality.

With the understanding that we absolutely need some phosphates in our tanks, the question becomes how much is too much, and how much is too little?

On one side of this coin you have phosphate deficiency, a problem very few of you will have. Signs of this will show up first in plants with symptoms like stunted growth, small / deformed new leaves, darkened coloration on older leaves (where it isn't supposed to be), poor rooting, and the appearance of GSA or green spot algae because your plants are too weak to combat it.

Conversely, excess phosphate is a problem nearly everyone will have at some point. While it isn't directly toxic to fish and invertebrates within reasonable levels, it can create algal blooms that will steal oxygen and cause pH instabilities that can be detrimental to fish health. These algal blooms are the hallmark of too much phosphate!

How much phosphate is too much? It depends to some degree on what you are keeping in your display. In a planted tank, 0.02 – 0.1 parts per million is a good range, and this will depend on how densely the tank is planted, how bright the lights are and whether you're supplementing carbon dioxide. The ratio of nitrate to phosphate is just as critical as the phosphate value and should be between 10:1 and 15:1. In an aquarium that doesn't feature plants, you should be shooting for a phosphate level from a barely measurable trace to 0.03ppm. This will allow for all the biological needs of your fish, inverts and bacterial filter (oh yeah, bacteria need phosphorus too) without giving fuel to excess algae growth.

If you find yourself fighting chronically high phosphate levels after testing with your handy Tropic Marin PO4 test kits, you'll need to start looking into where these phosphates are coming from. The prime culprit is overfeeding and/or low-quality food. Overfeeding is another article, but trusting your food supplier goes a long way to controlling unwanted nutrients. In house, we always feed Nutramar and Gamma foods. So, if you're not overfeeding, and you have a high-quality food and you're still fighting your test results, your issue might be in the water. Both well water and urban water systems can sometimes contain measurable amounts of phosphate, so measure it and if you have a problem, look into either getting a reverse osmosis filter, or sourcing your water from your local fish store. The last prominent source to look out for is décor. Some sand, rocks and even plastic castles can leach phosphates over time. Get your décor from your LFS!

We should all be well past the fear of phosphates so we can start looking at it like the fundamental nutrient it is for our aquariums. Just like anything else in our tanks, phosphate needs to be monitored and maintained in an appropriate range and ratio. Too little is bad for everything in that tank and too much is just as detrimental. If you have too much, check out our article on phosphate control. If you have too little, there are excellent solutions available to you for this as well through your Local Fish Store; tell them Aquatropic sent you. We're glad we had this talk, Don't fear the phosphate!