Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
Hi Roadrunner, welcome!
My phosphate test consistently reads 10+. But if I go by the test results and stop adding more, I soon see phosphate deficiencies in the plants, as well as green spot algae that indicates low phosphate.
I've tested the test, by mixing up solutions of phosphate and distilled water of known concentrations, and all those read perfectly. And it reads 1ppm with my tapwater, which I've verified with the water company is also correct. It's only with real tank water that I get results which are totally at odds with what's happening in my tank. It's a mystery I've never been able to explain.
I've been told many times never to put too much faith in tests. And I'm forced to agree. It's not a very satisfying answer, but that's the way it is.
Even if you really do have 5ppm of phosphate, that's usually not a problem. Granted, I have seen reports from people who had persistent algae problems, who found relief only with phosphate removers. But that's a fairly rare occurrence. Furthermore, most of these people usually have at least 3ppm of phosphate in their tapwater. That phosphate is in the form of orthophosphate, rather than the potassium phosphate we dose; and it seems to have different effects on a tank.
Chances are your problem lies elsewhere. In particular, your light/carbon ratio. At 65W, that sounds like a power compact (PC) fixture. I'm no good at estimating light levels for those, but I'm fairly certain that you'll have enough light that your plants require some form of supplemental carbon.
If you have high light, you need CO2; no way around it.
If you have medium light, CO2 will still provide the best plant growth. However, Seachem Excel is also an option. It doesn't provide nearly as much carbon as real CO2, but it can provide just enough at this light level to keep plants healthy, add to growth a fair amount, and prevent algae. Although it's not recommended if you keep anacharis or hornwort, and vals may suffer until they adjust.
If you tell us the distance between the bulb and substrate, hopefully someone with PC experience can tell if you have medium or high light.
Then, you'll need to decide whether to reduce the light level to low, or add either Excel or CO2 as necessary. DIY yeast CO2 is quite feasible on that size tank, if you don't mind mixing up some new yeast/sugar mix every week.
Once the light/carbon ratio is right, then we can work on the fert requirements; which will of course change along with changes in light/carbon.