Do not use the phosphate remover! Use your plants as a phosphate remover. Your plants need some phosphate to grow anyways
I think Skippy is right about the type of algae, but I am no algae expert. But, I have had many battles with it, and have been winning for a couple years now. It could just be a partial symptom of new tank syndrome, your tank is really pretty new. With that particular algae, the only time I saw it was when I got lazy on the water changes. How often/how much do you do water changes?
Other than that, the best way to combat algae is to create an environment where the plants can outcompete the algae. Its all about balancing everything out. I will go over the overview of what I have found in my experience. The four keys to that are:
1. Lighting
2. Nutreints
3. Water cleanliness(not the most accurate term,but..)
4. Planting density
1. Lighting, Intensity and spectrum are key here.
- Intensity, most people shoot for about 2 wpg as a target, more with CO2, less without CO2. You are about 1.6 of normal output flourescent light, which is on the low side, especially with a deep tank like a 90. But many people successfully grow some plants at that light level. You are limited to lower light plants. More light would help, IMO.
- Spectrum, the light must be in a spectrum that the plants can use. I don't know what your bulbs are but if the plants had been actually growing for three months I don't think you have the wrong spectrum. I don't know what that code means, can you list the brand and name of the bulb? Also, age is big factor in flourescent lighting, how are old are the bulbs?
2. Nutrients - Micros, Macros and Carbon. with more light you need more nutreints
** Micros = trace elements. Your plants need a vareity of trace elements including iron. Some people use a plant substrate to help the plants out and they work well. The other is liquid ferts, there are many prepared trace element fertilizers to use. The popular ones seem to be Seachem, Tropica Mastergrow and Kent. I use Seachem Flourish and I would suggest it to you. I would buy a bottle and start by dosing per the bottle directions twice a week. It is a little light on Iron, but with your ligthing I would suggest getting a Iron rich fertilizer tab and put it under the sword in the gravel. I use Seachem Flourish tabs. Swords are heavy root feeders and your gravel is giving them nothing.
** Macros = N,P,K
-N = nitrate, your plants need relatively small amounts of this to survive. In your setup I would think what you get from feeding your fish would be enough, but you say it tests out at zero. Are you sure about this. If it regularly does you will have to add some, but get the micros going first before you decide you need to add extra Nitrate, it can boost algae growth if the plants aren't growing fast enough to use it.
-P = Phosphate, once agian your plants need a small amount to survive, but much less than they do nitrate. Once again you shouldn't need to supplement this at first, nor is it necessarily the cause of your algae.
- K = Potassium - this is something your plants need and in a pretty decent amount. You can use Flourish Potassium, but it is expensive long term. You can buy Nu-salt(salt substitute) at the grocery store and doses 1/4-1/2tsp twice a week. I think this would help your plants a lot.
** Carbon = usually CO2. Plants are made mostly of carbon, so it makes sense to add a source of carbon to the tank. But, this only necessary if you have the light and other nutreints to use it. But, it will always help and won't hurt anything unless you put in too much and it harms the fish. You can use Pressurized CO2, DIY yeast/sugar CO2, or Seachem Excel. This is another post entirely if you want more info here, but it does not have to be difficult.
3. Water cleanliness= water changes. This is a key. I am now doing 50% a week on my tanks. But in your setup 25% should be fine. It seems like a pain at first, but, you will develop a system. A lot of people buy the python water change units to simplify it. Currently, I would do several 25-50% water changes a couple days a part to see if that helps clear the algae you currently have.
4. Plant density- the more the better. I would at least double the current stock of plants you have. Especially fast growing nutreint hungry plants like Anacharis,. With most stem plants you can prune off the top of the plant and replant the top leaving the base. New shoots should sprout on the base you left. That would be a way to double your stem plant density.
These are good places to start if you really want to grow your plants. I hope this helps.
