Black or Mustard Algae in my above ground pool with a heate?

[taras1]

Help please
note: i will get back to this when i bring my water in for testing and post it at a later date. didn't know this was needed. sorry
clorine highest on chart 10.5, total alak 90 ppm, total hardness 100 ppm, ph 7.4 or 7.5 hard to tell, my test but will bring water in for the rest of test. I do not know how to get free cl.
i had something that looked like sand on the bottom of the pool liner. It would sweep. I waited till it settled and vacumed it and a few hours later it was back. Did this many times and vacumed it slower. Even asked my grown son if he was playing tricks on me and putting sand in the pool. I didn't know about algae.
Finally found it called mustard algae after 2 years of discribing this to the pool stores. They told me they didn;t know what i was talking about. And finally i had a answer to the sand in my pool.
Did everything they told me to do but it came back.
Went to another pool store and did what they said and it came back.
Tried the third store and it came back, treated for mustard algae at that time. And all parts from the pool was treated also. Left in the pool.
This was many years ago and never got rid of it.
Now sometimes it looks black.

So is it now black algae (looks like it) or mustard or what- on the bottom of my pool?

Have a 15' above ground round pool with a vinyl liner.
I do use a hayward pool heater due to a medical condition called raynaud and i need warmer water. I also at times use a solar cover on top on the pool to keep the water warmer to save on electric of my heater. The heater is not connected at this time. I bypassed it till i corrected my water,
concern is now chem for algae maybe metals will corrode the heater.
I recently opened my pool for the summer and i was kind of sand look on the bottom. Water just alittle green. I checked the total alkilinity it;s good and shocked it with 2 bags which is a double dose i was told to do(from pool store) due to aklgae and adjusted the ph, did the cyanuric test and its good. Sweeped the walls and bottom of liner and vacumed it and black algae is growing on the bottom of the liner.
Does this mean i have algae in the sand under the liner? I run the pool 4 -6 hours daily. I use clorine tabs 3" with stabilizer in itin the floater. Have a earth filter hayward and pump with the fingers. I have spent so much on chem and did all requested to get rid of this. Including putting all tools and hoses in the pool and ended up with shock stuck stuck on parts because they didn't give me good info. They seem to test my water and tell me to put in to much of whatever then reverse it and tell me to add chem to reverse it. Selling me more chem that i do not need till i found i do the testing myself and am better off but bring my water in a few times over the summer to check and correct it but carefully.
I will get back to this after i bring in the water for testing and enter thatthe chem. my chol level is still very high.
When i vacumme the brown or black from the bott6om of the pool maybe it moves around and i am not getting it all and then it settles again?
I have my second heater now and am concerned about chem that will corrode it or my chem being off and dammageing it also.or metals going in for algae treatment. Now regarding the algae treatment metals arwe not good for the heater,
i really do not know what to do?
Can i get rid of this on the bottom of my vinyl liner or not?
How do i do this?
How or can i prevent it from coming back if i can get rid of it because in ny i need to heat my water to about 90 degrees and a neighbors tree blocks the sun somewhat.
How do i get rid of the metals so i can put the water through my heater to warm the water and not corrode the heater. Maybe should of gotten a spa instead of a pool but can;t afford to change all this now. .
Please if you have info for me please respond.
Also it took me 3 hours to find out where i have to go to post a question. Can anyone tell me details as to where you have to go on this sight to post a question. I am a senior and not so good on comp. And couldn't get contact info to ask and it said something about relavance or something and couldn;t figure all this out no mater what i tried , i searched black algae on above groung pool and then didn't know what to do.
Thanks so much. Glad to find this sight and am hopeful in more than one way due to scleroderma and that is for hope also.
Hope i can figure how to get back to my post also.
Can;t tell you how much money spent and chem was added to my pool.
Thanks so much for your help