Akasha, you are a very knowledgeable and dedicated fish keeper. These little setbacks are frustrating, I know. But we can beat them.
I cannot offer anything on the phosphate issue, other than to say that I believe there is filter media that can deal with this. I'll leave this for the more expert on this topic. Same for the flukes...I rarely enter disease threads because of my limited knowledge and experience in that area. But I can hopefully ease your mind on the sand/pH issue.
I have tanks in which the pH is well below 5 [my lowest kit tests 5.0 and above, and it is much more yellow than even the 5 colour], and others where it remains in the mid-6 range. My tap water is 7.0 or 7.2, achieved by the addition of sodium carbonate (commonly, soda ash) and calcium hydroxide (lime). The latter is a new addition; the former (soda ash) has been added since 2001. These are added to maintain a higher pH to avoid pipe erosion; there is basically zero GH and KH, so no buffers in the source water. I have been doing 50-60% water changes continually, but they impact little on the individual tanks' pH. I did a succession of pH (and GH) tests pre and post water change and for successive days for several weeks so I am fairly confident of this.
The fluctuation in pH is not as much of an issue as many think, provided it is not drastic. If I were you, I would do a series of tests like I did, and see where the numbers fall. Bear in mind too, that GH/KH is actually the more important, and these are not likely to change much if at all unless you are specifically targeting them with buffers of some sort [which I will not use]. The biological stability that will establish in an aquarium with regular partial water changes, and assuming stocking and feeding are relative to volume, is fairly resistant.
Ask any questions if you'd like me to explain my processes/tests further.
I cannot offer anything on the phosphate issue, other than to say that I believe there is filter media that can deal with this. I'll leave this for the more expert on this topic. Same for the flukes...I rarely enter disease threads because of my limited knowledge and experience in that area. But I can hopefully ease your mind on the sand/pH issue.
I have tanks in which the pH is well below 5 [my lowest kit tests 5.0 and above, and it is much more yellow than even the 5 colour], and others where it remains in the mid-6 range. My tap water is 7.0 or 7.2, achieved by the addition of sodium carbonate (commonly, soda ash) and calcium hydroxide (lime). The latter is a new addition; the former (soda ash) has been added since 2001. These are added to maintain a higher pH to avoid pipe erosion; there is basically zero GH and KH, so no buffers in the source water. I have been doing 50-60% water changes continually, but they impact little on the individual tanks' pH. I did a succession of pH (and GH) tests pre and post water change and for successive days for several weeks so I am fairly confident of this.
The fluctuation in pH is not as much of an issue as many think, provided it is not drastic. If I were you, I would do a series of tests like I did, and see where the numbers fall. Bear in mind too, that GH/KH is actually the more important, and these are not likely to change much if at all unless you are specifically targeting them with buffers of some sort [which I will not use]. The biological stability that will establish in an aquarium with regular partial water changes, and assuming stocking and feeding are relative to volume, is fairly resistant.
Ask any questions if you'd like me to explain my processes/tests further.