First off, having film algae on the glass of your tank is natural and will occur on a weekly basis. You will need to grab some sort of algae glass scraper to be able to maintain clean glass. Some snails can help, but IMO nothing beats the clarity of weekly cleaning of the glass with a scraper.
You have been provided sound advice from those who have already posted. I will share with you some of my detailed notes on phosphate that I have collected over the years below. All of the below info I have shared on this forum in prior posts. One thing to remember is that you are in a hobby where the more you can understand what is going on in your system the more success you will have over time. I provided some hyperlinks to help you with further reading.
Algae grow with nutrients and light. Some lighting conditions can cause an algae outbreak, but many times it comes down to controlling nutrients, and in particular controlling phosphates.
Kinds of Phosphate found in Aquariums
Phosphates exist in three forms: orthophosphate, metaphosphate (or polyphosphate) and organically bound phosphate; each compound contains phosphorous in a different chemical arrangement.
These forms of phosphate occur in living and decaying plant and animal remains, as free ions or weakly chemically bounded in aqueous systems, chemically bonded to sediments and soils, or as mineralized compounds in soil, rocks, and sediments.
The phosphate that is of most interest to aquarist is Orthophosphate and organic phosphate. Orthophosphate is a readily available to the biological community. Organic phosphates are typically estimated by testing for total phosphate. The organic phosphate is the phosphate that is bound or tied up in algae/plant tissue, fish waste, or other organic material like fish food. After decomposition, this phosphate can be converted to orthophosphate. It is a cycle. Marine Phosphorus cycle here:
http://www.azimuthproject.org/azimuth/show/Phosphorus+cycle
Phosphate in the food you feed your fish
Foods are by far the most important source of phosphate in most aquariums.
You can read more about it here:
http://www.advancedaquarist.com/2012/3/chemistry
Phosphate in Rock and Substrate
There is also some discussion on phosphorus leaching from rocks into our aquariums. Over time (anywhere from a year to several years) this will slow down or cease. Much discussion has occurred on forums regarding this. A lot is anecdotal.
What is known is what occurs in natural systems, and a few have jumped on this as a way of explaining what may be also playing out in our tanks.
http://sciencelearn.org.nz/Contexts...ience-Ideas-and-Concepts/The-phosphorus-cycle
What is known is that aragonite can act as a reservoir for phosphate. This reservoir can make it difficult to completely remove excess phosphate from a tank that has experienced very high phosphate levels, and may permit algae to continue to thrive despite cutting off all external phosphate sources. In such cases, removal of the substrate may even be required. Likewise, phosphate can precipitate onto the surface of calcium carbonate, such as onto live rock and sand.
http://www.advancedaquarist.com/2002/4/chemistry
Dead reef rock (also referred to as base rock), tufa rock, but also crushed coral substrate may contain serious amounts of phosphates. Some is bound very tight (pretty dissoluble minerals), some may be dissolved given the proper biochemical environment. If you want to know approximately how much soluble phosphate is contained in a specific rock or substrate, it is possible to test it in a bucket with heated and moved salt water for some days. Contents of 1 mg phosphate per kilogram of rock or crushed coral, and higher have been determined that way. A tank in which such rock is used will have high phosphate concentrations for a long time. If phosphate rich rock material is already in your system, there are two possible solutions: Take out the rocks, or increase the phosphate output of your system (see below on how to control and export phosphate).
Testing for Phosphate
When it comes to phosphates, tests kits aren't telling you the whole truth of what is in your tank.
http://packedhead.net/2014/skeptical-reefkeeping-ix-test-kits-chasing-numbers-and-phosphate/
Testing for phosphate is complicated. One can readily test for one of the common forms of phosphorus in reef tanks, inorganic orthophosphate, but testing for organic phosphorus compounds is considerably more tedious. Moreover
, if there is an algae “problem”, then the algae may be consuming the phosphate as fast as it enters the water, masking the issue. Consequently, reef keepers may not recognize that they have a phosphorus problem, only that they have an algae problem. This article describes some of the issues around phosphorus in reef tanks, including the forms that it takes, its origins, ways to test for it, and most importantly, ways to export it.
http://www.advancedaquarist.com/2002/9/chemistry
What can you do to control phosphate and algae growth?
Algae growth is a normal part of keeping aquariums. It is something that should be managed as you can't completely get rid of all algae types and growth. What you want to be able to do is manage it in a way where it isn't taking over the tank.
-- Use RODI water for mixing salt water and in the ATO. Limit the amount of phosphates being added to the tank.
-- Don’t overfeed. Make sure all food is consumed and not falling to the bottom of the tank to decay. Again, this is to help to limit the amount of phosphates being added to the tank.
-- If you are feeding frozen foods like krill, mysids, or brine shrimp, first thaw and rinse the food in either tank water or RODI water. The liquid in which these food are frozen can contain high levels of phosphates.
-- Use a skimmer. Keep up on maintenance for it to work efficiently and effectively. Skimming can take out organic phosphates. (
http://www.advancedaquarist.com/2010/10/aafeature)
-- Use GFO as a way to pull phosphorus out of the water. There are many brands on the market. (
http://www.advancedaquarist.com/2004/6/review) (
http://www.advancedaquarist.com/blo...osphate-removal-than-other-phosphate-removers) (
http://www.advancedaquarist.com/2012/2/chemistry)
-- Do weekly 10-15% water changes for several months to start to bring your phosphate levels down (some people bump up weekly water changes to 20% for a little while to get it in check). Siphon the sand bed with water changes and harvest all algae out of the tank. Phosphates that are bound up in algae can be pulled out of the tank can help to limit the amount of phosphorus that is being incorporated to the phosphate cycle that is happening in the tank.
-- Buying a combination of CUC to help to manage algae growth until you can get phosphate in check. Do research to target the CUC that will eat the algae that you are having issues with.
-- Some phosphates can be harvested by macroalgae, as such some aquarists use
Chaetomorpha sp. macroalgae to help to lower phosphate levels.
I’m sure there are other things that can be added to this list, my list grows over time.
I would do all of the above to get a handle on your phosphate levels. And then once you have things better managed then you can decide to back off of a couple of items above (e.g. GFO or the amount of water changes you are doing).
Managing phosphate and algae is something that all reef keepers must do during the life of keeping their reef tanks. I hope you find this helpful, if not thought provoking.
