There are as many ways to have poor CO2 as there are the number hobbyists. What you need to do is to go down the list of possible indirect causes until you arrive at the solution that works for you. I totally agree that shrimp should be used as ornaments and not as a solution to the algal bloom, because shrimp cannot possibly solve the problem of poor CO2, and neither can they solve the indirect causes such as poor flow/distribution.
It's a short list. The better solutions arise in in the following order:
1. Is there too much light? Reduce the lighting intensity immediately when you have an algal bloom. Too much light is the preeminent causal factor that drives the demand for CO2 and nutrients. Either remove/disable a bulb or find some way of obscuring the light either via floating plants or an external obfuscation.
2. Examine flow and distribution. Do you have approximately 10X flow rating? If not, consider upgrading either the filter or the supplemental pump(s). If the flow rating is sufficient then consider the distribution method. You may need to rearrange the location of the outlets and pumps. Observe the plant leaves to ensure that they are gently rocking in the "breeze". Ensure that all outlets are pointing in the same direction and that there is even energy across the width of the tank.
3. Examine gas diffusion technique. An injection rate increase is called for. This has to be accomplished carefully if there are fish in the tank. If there are no fish in the tank then the increase can be done immediately and it can be as high as necessary to satisfy the plants demand for CO2. How is the diffusion being accomplished? If by in-line device. make sure that the tubing of the inlet and outlet spuds are not restricting flow, i.e. the internal diameter of the spuds should be no smaller than the ID of the filter outlet spud. If the diffusion method is in-tank then experiment with relocation of the the diffuser, such as below the spraybar or possibly even being fed directly into the inlet of the supplemental pump.
4. Supplement the injection with any of the liquid carbon products, at least in the short term.
i have high phosphates in my tap water so was struggling with algae, the amano accompanied by some flying foxes do a great job at keeping everything tidy, well apart from the grass but its green algae that I have in that situation.
High phosphates have absolutely nothing to do with algae. In fact, it is much more likely that if you think that, then you don't have enough phosphate and you should immediately implement a dosing program that includes PO4.
Also, to me your drop checkers are suggesting that you are injecting too much co2 as they should be green rather than yellow... however, ceg4048 appears to know his stuff from the forums so again I may be wrong.
Yes, regrettably, you are wrong. Algae never results when the CO2 is too high. The only reason the expression "too much CO2" is even relevant is because too much CO2 is toxic to fish, never to plants.
...that more plants will use up the nutrients before the algae can, therefore over powering the algae...
This can never happen and we suggest that you abandon this line of thought because it always leads to disaster. Plants can never compete with algae for nutrients. Algae are predatory and they wait for the plants health to fail, then they attack. They can easily feed on the nutrients being released by the plant leaves as the leaves disintegrate.
Cheers,