SCUBA tanks are not practical for refilling most modern airguns. The limit that you are experiencing is due to the equalization pressure of the SCUBA tank and bottle being below the desired fill pressure. If your SCUBA tank starts at 232 bar, the maximum pressure that you could possibly reach on your rifle would be ~215 bar for the first fill (this is a rough guess for conceptual purposes, there are calculators that you can use to get an accurate pressure change per fill). The exact equalization pressure will depend upon what pressure your rifle is starting at and the volume of the bottle/cylinder. The subsequent refill will start from a lower pressure (215 bar as per this example).
Since many guns have fill pressures of 230-250 bar, a 230 bar SCUBA tank will only provide so many partial refills. This is especially true on rifles with large bottles, like the impact. A 300 bar SCBA tank would be more practical, if you need air and don't have access to a compressor. A personal compressor (like a GX CS3 or JTS comp1) would be more practical, as you can skip the SCUBA tank all together and always get a full fill.